CHAPTER 5

Circulatory System

In o rde r t o m a k e t h e b l o o d vessels m o r e easi ly v i s ib le , t h e a r te r ies a n d ve ins are usua l ly i n jec ted w i t h c o l o r e d la tex. D o u b l y i n j ec ted f r o g s usua l l y have red latex in the i r a r ter ies a n d b lue la tex in t he i r ve ins ; t r i p l y i n jec ted f r o g s usua l l y have t he ar ter ies in red , t he p u l m o n a r y a n d sys tem ic ve ins in b lue , a n d t h e renal a n d hepa t i c po r ta l sys tems in ye l l ow . In o r d e r t o m a k e these i n j ec t i ons , y o u r f r o g was p r o b a b l y cu t by t h e s u p p l y h o u s e in at least t w o p laces : ac ross t h e ches t r e g i o n , in o r d e r t o reach t h e hear t , a n d a l o n g t h e t h i g h , in o rde r t o reach t he sc ia t i c ve in .

(Advanced s t u d e n t s may w i s h t o no te tha t t he ar ter ies are i n j ec ted in t h e d i r ec t i on of b l o o d f l o w , b e g i n n i n g at t h e hear t ; t h i s i n j e c t i o n is usua l l y p e r f o r m e d f i rs t , t o p reven t t h e f i l l i ng of t h e ar te r ies w i t h b l ue la tex d u r i n g t h e v e n o u s i n j ec t i on . T h e p u l m o n a r y a n d sys tem ic ve ins are t h e n i n j ec ted in t he d i r ec t i on o p p o s i t e t o b l o o d f l ow , b e g i n n i n g at t he s i nus v e n o s u s . Th i s i n j ec t i on mus t be p e r f o r m e d w i t h su f f i c i en t f o r c e t o b reak t h r o u g h t h e va lves ; o f ten the wa l l s of t h e ve ins r u p t u r e i ns tead , a n d t h e b o d y cav i ty b e g i n s t o f i l l w i t h t he latex. The po r ta l sys tems are i n jec ted t h r o u g h t h e sc ia t i c ve in , largely in t h e d i r e c t i o n of b l o o d f l o w . Co l la te ra l c i r c u l a t i o n in t h e leg f i l l s t h e f e m o r a l ve in . T h e hepa t i c po r ta l ve in a n d its t r i bu ta r i es m u s t f i l l in a d i r e c t i o n o p p o s i t e t o t ha t of b l o o d f l o w ; t he f i l l i ng of t hese vessels is o f t en p o o r as a result .)

A l l s t uden t s s h o u l d be ca re fu l t o n o t i c e tha t , w h i l e a r te r ies branch i n to f iner a n d f i ne r b l o o d vessels , ve ins c a n m o r e o f ten be d e s c r i b e d as c o m p a r a b l e t o a sys tem of r ivers , w i t h sma l le r ve ins ( l ike sma l l e r s t reams) be ing tributaries, no t b r a n c h e s , of t h e la rger ones . (The po r ta l ve ins are e x c e p t i o n a l , s i nce they do b ranch . ) A l so n o t i c e tha t a r te r ies supply b l o o d to t he o r g a n s w h i c h they serve, w h i l e ve ins drain b l o o d from t hese o r g a n s .

The b l o o d vessels , pa r t i cu la r l y t he ve ins , are ra ther va r iab le . T h e pa t te rn of b r a n c h i n g s a n d r e g r o u p i n g s d e s c r i b e d b e l o w may d i f fe r f r o m tha t obse rved in y o u r o w n f r o g . (In pa r t i cu la r , it is no t u n c o m m o n at al l f o r t h e t r i bu ta r i es t o a ve in t o j o i n t in a d i f f e ren t o r d e r ; it is a b i t less c o m m o n fo r t he b ranches of a r ter ies t o ar ise in a d i f f e ren t order . )

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66 A Labo ra to r y G u i d e t o F rog A n a t o m y

A. HEART

If y o u have no t a l ready d o n e so , cu t t h r o u g h t he ven t ra l b o d y w a l l , i n c l u d i n g the s h o u l d e r g i rd le , a n d e x p o s e t h e hear t . T h e hear t is s u r r o u n d e d by a t h i n , m e m b r a n o u s per icardium (Greek : per / - , " a r o u n d " or " s u r r o u n d i n g " ; cardia, " h e a r t " ) , w h i c h y o u have p r o b a b l y a l ready cu t .

Move the hear t f r o m s ide t o s ide a n d obse rve t h e s inus venosus b e h i n d it on t he dorsa l wa l l of t h e pe r i ca rd ia l cav i ty . T h e s i nus v e n o s u s is f o r m e d by t h e t w o s u p e r i o r venae cavae, w h i c h a p p r o a c h f r o m t h e s ides , a n d t h e i n fe r i o r vena cava, w h i c h a p p r o a c h e s f r o m f u r t h e r pos te r io r l y . These t h ree ve ins g ive a t r i angu la r shape t o t he s inus venosus . B l o o d f l o w s f r o m t h e s i nus v e n o s u s in to t he r igh t a t r i u m of t h e hear t . T h e o p e n i n g is g u a r d e d by a pa i red va lve, t h e sinoatrial va ive , w h i c h p reven ts b a c k f l o w .

T h e hear t i tself cons i s t s of t w o atr ia ( s ingu la r , atrium; a lso f o r m e r l y ca l led auricles) and a s ing le ventr icie. T h e r igh t a t r i u m rece ives b l o o d f r o m t h e s i nus venosus . The left a t r i u m rece ives b l o o d f r o m t h e l ungs . F r o m t h e t w o a t r ia , b l o o d en ters t he s ing le ven t r i c l e t h r o u g h t h e atr ioventr icular va ive . D u r i n g c o n t r a c t i o n of t h e ven t r i c le , t h i s va lve c loses t o p reven t b a c k f l o w .

T h e ventr icle is t h e c o n i c a l , pos te r i o r l y d i r ec ted c h a m b e r of t h e hear t . S ince it mus t p rope l t he b l o o d t h r o u g h o u t t h e rest of t h e body , t h e ven t r i c l e possesses a t h i c k , m u s c u l a r w a l l . T h e semi lunar va lves g u a r d t h e passage f r o m the ven t r i c l e t o t h e t r u n c u s a r te r iosus . T h e t runcus ar ter iosus (or conus arteriosus) is a s tou t , cy l i nd r i ca l vessel w h i c h car r ies t he b l o o d away f r o m t h e hear t .

B. ARTERIES

U p o n leav ing t he hear t , t h e t r u n c u s a r te r i osus runs an te r io r l y , b r a n c h i n g in to t h ree pa i rs of a r te r ies : t he r i gh t a n d left pu lmocutaneous ar ter ies ( the m o r e pos te r i o r pa i r ) , t he r i gh t and left systemic ar ter ies ( the m i d d l e pa i r ) , a n d

T h e ar ter ies , pa r t i cu la r l y t h e la rger ones , are c i r cu la r in c ross s e c t i o n a n d the i r wa l l s are t h i ck . T h e ve ins , by con t ras t , may o f ten have i r regu la r c ross sec t i ons w h i c h c o n f o r m t o f i l l t h e space b e t w e e n s u r r o u n d i n g o r g a n s . T h e wa l l s of t h e ve ins are t h i n and latex is a lways v is ib le t h r o u g h t h e m . Un in j ec ted ve ins t e n d t o co l l apse , w h i l e u n i n j e c t e d ar te r ies usua l l y re ta in the i r shape . S ince t he f l o w of v e n o u s b l o o d is usua l ly s lower , a ve in d r a i n i n g an o r g a n w i l l genera l l y have a la rger c ross sec t i on t h a n t h e ar tery s u p p l y i n g tha t same o r g a n . If t h e necessary s l ide mate r ia l is ava i lab le , e x a m i n e a n d c o m p a r e m i c r o s c o p i c c ross sec t i ons of a r ter ies a n d ve ins . Y o u may a lso at th is t i m e w i s h t o e x a m i n e s l ides of va r i ous types of b l o o d , b l o o d - f o r m i n g ( hemopo ie t i c ) t i ssues , a n d l y m p h .

C i r c u l a t o r y Sys tem 67

t he r igh t a n d left c o m m o n carot id ar ter ies m o s t an te r io r l y . Each c o m m o n ca ro t i d immed ia te l y sp l i t s i n to sepa ra te internal a n d ex terna l carot id ar ter ies. These f i rs t f ew b r a n c h i n g s o c c u r in rap id s u c c e s s i o n , a n d may f r e q u e n t l y vary : t h e sys temic a n d c o m m o n c a r o t i d a r te r ies may be c o n j o i n e d , f o r e x a m p l e , a n d the d i s t ance cove red by t he c o m m o n c a r o t i d be fo re its f i rs t b r a n c h i n g may be l o n g , sho r t , o r nonex i s ten t .

1 . The pu lmocutaneous artery, a r i s ing f r o m t h e t r u n c u s a r te r i osus , s o o n b r a n c h e s in to a m o r e an te r i o r cu taneous artery a n d a m o r e p o s t e r i o r pulmonary artery o n e i the r s ide of t h e body . T h e p u l m o n a r y ar te r ies supp l y b l o o d t o t h e l u n g s ; t h e c u t a n e o u s ar te r ies rami fy j us t b e n e a t h t he su r face of t he mo is t s k i n . T h e e x c h a n g e of gasses ( o x y g e n , c a r b o n d iox ide ) takes p lace b o t h t h r o u g h t h e sk in a n d t h r o u g h t he a lveo l i of t he l ungs . (Advanced s t u d e n t s s h o u l d f o l l o w o n e of t h e c u t a n e o u s ar ter ies , and obse rve tha t it b r a n c h e s in to dorsa l , lateral , a n d anter ior rami . T h e an te r i o r r a m u s g ives off a ramus auricular is t o t h e t y m p a n i c r eg i on , a n d f ina l l y c o m m u n i c a t e s w i t h t h e t e m p o r a l ar tery , d e s c r i b e d be low , t o s e n d b l o o d in to t h e supe r f i c i a l pa r ts of t h e face.)

2. The external carotid artery is t h e m o r e med ia l a n d m o r e supe r f i c i a l of t he c a r o t i d ar ter ies . It supp l i es b l o o d t o t h e t o n g u e a n d t h e f l o o r of t h e m o u t h . (Advanced s tuden t s s h o u l d f o l l o w t h e ex te rna l c a r o t i d a n ­te r io r l y , w h e r e it g ives off m a n y sma l l b r a n c h e s t o t h e m u s c l e s s u r r o u n d i n g t he h y o i d appa ra tus , f ina l l y c o n t i n u i n g as t h e l ingual artery benea th t he t ongue . )

3. T h e internal carot id artery is s o m e w h a t la rger t h a n t h e ex te rna l c a r o t i d and is s i tua ted m o r e la tera l ly a n d a lso deeper . T h e in te rna l c a r o t i d , o r s o m e t i m e s t h e c o m m o n c a r o t i d , has a b u l b l i k e s w e l l i n g at i ts base , t h e so-ca l led carotid bulb. Th i s b u l b swe l l s a n d c o n t r a c t s e las t ica l l y t o insure tha t t he b ra in a n d o the r head s t r u c t u r e s rece ive a m o r e s teady, even b l o o d p ressure , ra ther t h a n a p u l s a t i n g one . (Advanced s t u d e n t s s h o u l d f o l l o w t h e in te rna l c a r o t i d as it r uns an te r i o r l y f r o m t h e c a r o t i d b u l b t o en te r t h e head , g i v i ng of f f i r s t a cerebra l ar tery t o t h e b r a i n , a n d an ophthalmic artery t o t he eye r e g i o n ; t h e o p h t h a l m i c ar te ry may ar ise e i ther f r o m t h e ce reb ra l ar tery , o r d i rec t l y f r o m t h e in te rna l c a r o t i d . T h e ce rebra l ar tery a lso g ives of f a r amus posterior, w h i c h runs p o s t e r o m e -d ia l ly t o meet w i t h its pa r tne r of t h e o p p o s i t e s ide t o f o r m t h e m e d i a n , u n p a i r e d basi lar artery, w h i c h supp l i es b l o o d t o t h e sp ina l c o l u m n . B e y o n d t h e ce reb ra l a n d o p h t h a l m i c ar ter ies , t he in te rna l c a r o t i d c o n t i n u e s as t h e pa la t ine ar tery , s u p p l y i n g b l o o d t o t h e roo f of t h e m o u t h , a n d g i v i ng of f a b r a n c h w h i c h f o r m s a l oop r e a c h i n g t o t he max i l l a ry a r te ry ; a pa la tonasa l ar tery a r ises f r o m th i s loop. )

4. The systemic arter ies ar ise f r o m t h e t r u n c u s a r te r i osus . A f te r sp l i t t i ng away f r o m t h e c a r o t i d ar te r ies , t he sys tem ics t u r n la tera l ly a n d t h e n dorsa l l y t o f o r m t h e r i gh t a n d left aortic a rches . Each ao r t i c a r ch g ives

68 A Labo ra to r y G u i d e t o F rog A n a t o m y

off, in s u c c e s s i o n , a sma l l la ryngeal artery, a la rge occipl tovertebral artery, a n d a la rger subclav ian artery. (Advanced s t u d e n t s s h o u l d loca te t h e very sma l l la ryngeal artery, w h i c h ar ises j us t b e y o n d t h e c a r o t i d ar ter ies . It supp l i es b l o o d t o t h e la rynx a n d t h e a n t e r i o r m o s t par t of t h e esophagus . )

5. T h e occipl tovertebral artery ( for a d v a n c e d s t u d e n t s on ly ) supp l i es b l o o d t o t he e s o p h a g u s , t h e head a n d j aws , t he do rsa l b o d y wa l l , t he a b d o m e n , a n d t h e b ra i n (via t h e ve r teb ra l c o l u m n ) . T h e e s o p h a g e a l artery, t o t h e e s o p h a g u s , is g i ven off f i rs t . Jus t b e y o n d t h i s b r a n c h , t h e r ema inde r of t h e o c c i p l t o v e r t e b r a l a r tery b i f u r ca tes i n to a m o r e an te r i o r occipital ar tery a n d a m o r e p o s t e r i o r dorsover tebra l ar tery .

T h e occ i p i t a l a r tery runs in to t h e h e a d , w h e r e it b r a n c h e s in to an orbi tonasal artery and a s o m e w h a t la rger t empora l a r tery . T h e lat ter a r ches ven t ro la te ra l l y t o f o r m a l o o p w h i c h f ina l l y un i tes w i t h t he r a m u s an te r i o r of t h e c u t a n e o u s ar tery . F r o m th i s a r c h o r l o o p ar ise t h e internal mandibular artery t o t he inner m a r g i n s of t h e l o w e r j aw , t h e externa l mandibular ar tery t o t h e o u t e r m a r g i n s o f t h e s a m e , a n d t h e maxil lary, o r superior maxi l lary artery, a l o n g t h e m a r g i n s of t h e u p p e r j aw .

T h e dorsover tebra l ar tery g ives of f a r amus cranial is , o r ver tebra l artery, w h i c h runs dorsa l l y t o w a r d t h e ve r teb ra l c o l u m n t o meet t he bas i la r ar tery a l o n g t h e do rsa l m i d l i n e . Th i s p rov ides a n o t h e r r ou te by w h i c h b l o o d may reach t h e b r a i n . T h e r e m a i n d e r o f t h e d o r s o v e r t e b r a l ar tery c o n t i n u e s a l o n g t he do rsa l s ide of t h e b o d y cav i ty , pa ra l l e l i ng t he ver tebra l c o l u m n , a n d s u p p l y i n g a ser ies o f abdomina l ar ter ies t o t h e musc les of t h e a b d o m i n a l w a l l . Sma l l e r b r a n c h e s are a lso g i ven of f med ia l l y t o t h e musc les of t h e sp ina l c o l u m n a n d ad jacen t do rsa l r eg i ons ; s o m e of t hese b r a n c h e s c o m m u n i c a t e w i t h t h e l u m b a r ar te r ies in t he l u m b a r r e g i o n .

6. The subclavian artery supp l i es t h e musc les of t h e s h o u l d e r a n d f o r e l i m b ; t race it t o a p o i n t j us t b e y o n d t h e s h o u l d e r j o i n t , w h e r e it en te rs t he a r m . (Advanced s t u d e n t s s h o u l d c o n t i n u e fu r t he r , f o l l o w i n g t h e subc lav ian ar tery in to t h e a r m , w h e r e it b e c o m e s t h e brachia l artery. The b rach ia l a r tery b i f u rca tes jus t p r o x i m a l t o t h e e l b o w in to separa te radial a n d ulnar ar ter ies , r u n n i n g para l le l t o o n e a n o t h e r a l o n g t he fo rearm. )

T h e dorsal aorta is f o r m e d by t h e u n i o n of t h e r i gh t a n d left ao r t i c a rches . As it cou rses pos te r io r l y , it g ives of f t h e f o l l o w i n g b r a n c h e s (Nos. 7 -10) , in o rde r :

7. The coe l iacomesenter ic artery ( unpa i red ) , w h i c h d i v ides i n to a coe l iac and an an te r i o r mesen te r i c ar tery. T h e coel iac artery d i v ides f u r t he r i n to a hepat ic artery t o t h e l iver, a n d a gastr ic artery s u p p l y i n g the s t o m a c h a n d panc reas . T h e anter ior mesenter ic artery g ives of f a

C i r c u l a t o r y Sys tem 69

C. VEINS

1. Pulmonary Circulation

T h e pu lmonary veins r e tu rn f resh ly o x y g e n a t e d b l o o d f r o m t h e l u n g s t o t h e left a t r i u m of t h e hear t . They usua l l y j o i n t o g e t h e r f i rs t a n d t h e n e n t e r t h e hear t as a s ing le vesse l .

2. Systemic Circulation

Th is is m o r e readi ly s t ud i ed by t r a c i n g t h e ve ins b a c k w a r d f r o m t h e s i nus venosus .

The anter ior v e n a cava , o r p recava l ve in (pa i red) d r a i n s b l o o d f r o m t h e an te r i o r r eg ions of t h e body , i n c l u d i n g t h e head a n d f o r e l i m b s . Its t h ree t r i bu ta r ies , al l la rge, a re :

sp len i c o r l ienic artery t o t h e sp leen (La t in n a m e , / /en) , a n d t h e n b i f u rca tes in to an intestinal artery, t o t h e sma l l i n tes t ine , a n d a l iemorrhoidal artery, t o t h e la rge in tes t ine .

8. T h e urogenita l ar ter ies (s ix pa i rs ) , w h i c h s u p p l y t h e k idneys , g o n a d s , a n d fat bod ies . A l l s ix pa i rs may be t e r m e d renal ar ter ies {ren m e a n s k idney in Lat in ) , bu t on l y t h e f i rs t pa i r o r t w o g ive of f geni ta l (ovar ian o r spe rma t i c ) ar ter ies t o t h e g o n a d s .

9. The lumbar ar ter ies (several pa i rs) , w h i c h o r i g i n a t e a l o n g m u c h of t h e l eng th of t h e do rsa l ao r ta , espec ia l l y in t h e l u m b a r r e g i o n ( the " s m a l l o f t he b a c k " ) . These ar te r ies s u p p l y t h e do rsa l b o d y w a l l , t h e s e g m e n t a l musc les , a n d t h e ve r teb ra l c o l u m n ; they a lso c o m m u n i c a t e w i t h b r a n c h e s of t h e do r sove r t eb ra l ar tery .

10. T h e posterior mesenter ic artery ( unpa i red ) , w h i c h ar ises f r o m t h e do rsa l ao r ta at t h e pos te r i o r e n d of t h e c o e l o m . It supp l i es t h e pos te r i o r e n d of t h e la rge in tes t ine , a n d a lso t h e c l oaca .

1 1 . T h e do rsa l ao r ta n o w b i f u r ca tes , f o r m i n g a pa i r o f c o m m o n iliac ar ter ies. Each c o m m o n i l iac g ives r ise t o t w o b r a n c h e s (hypogas t r i c a n d ep igas t r i c ar ter ies) be fo re i tsel f b i f u r c a t i n g . T h e hypogastr ic artery (pa i red) supp l i es t h e u r i na ry b l adde r ; t h e epigastr ic artery (pa i red) supp l i es t h e ven t ra l b o d y w a l l .

Each c o m m o n i l iac ar tery t h e n b i f u r ca tes , c o n t i n u i n g as a sma l le r f e m o r a l a n d a la rger sc ia t i c ar tery . T h e f emora l artery (external i l iac artery) r uns a l o n g t he ou te r s ide o f t h e t h i g h , a n d s u p p l i e s t h e e x t e n s o r musc les (bas ica l ly ) of t h i s r e g i o n . T h e sciatic artery ( internal iliac artery) r uns a l o n g t h e p o s t e r o m e d i a l m a r g i n o f t h e t h i g h , s u p p l y i n g no t on ly t he f l exo r m u s c u l a t u r e (genera l ly ) of t h i s r e g i o n , bu t a lso t h e en t i re s h a n k a n d foo t .

70 A Labo ra to r y Gu ide t o F rog A n a t o m y

(a) The external jugular ve in , t he mos t an te r i o r of t h e th ree , f o r m e d by t he c o n f l u e n c e of t he l i ngua l a n d m a n d i b u l a r ve ins . T h e l ingual ve in d ra ins t h e t o n g u e a n d t h e f l o o r of t h e m o u t h ; t h e mandibular ve in , l oca ted m o r e latera l ly , d ra ins t h e b l o o d f r o m the reg ion of t h e l owe r j aw .

(b) T h e innominate ve in , f o r m e d b y t h e c o n f l u e n c e o f t h e s u b s c a p u l a r a n d in te rna l j u g u l a r ve ins . T h e internal jugular ve in d ra i ns b l o o d f r o m t h e b r a i n ; t he subscapular vein d ra ins b l o o d f r o m t h e s h o u l d e r a n d par t of t he f o r e l i m b .

(c) T h e subclav ian vein , t he m o s t pos te r i o r o f t he t h ree , f o r m e d by t h e c o n f l u e n c e of t he b rach ia l a n d m u s c u l o c u t a n e o u s ve ins . T h e brachial vein d ra ins b l o o d f r o m t h e a r m . T h e muscu locutaneous vein d ra ins b l o o d f r o m t h e musc les o n t h e la tera l s ide o f t h e t r u n k in t h e s h o u l d e r r eg i on , a n d a lso f r o m t h e many s u b c u t a n e o u s vessels in t he reg ion s u p p l i e d by t h e c u t a n e o u s ar tery . F r o m t h e head a n d s h o u l d e r reg ions , t h e m u s c u l o c u t a n e o u s ar tery runs pos te r i o r l y t o a p o i n t a b o u t m i d w a y a l o n g t h e body cavi ty , t h e n it reverses its d i r e c t i o n t o run an te r io r l y a n d j o i n t he subc l av i an .

T h e posterior v e n a cava , o r postcaval ve in (unpa i red ) runs an te r i o r l y a l o n g t he dorsa l wa l l of t h e body cavi ty . It is f o r m e d by t he c o n f l u e n c e of t h e f o u r pa i rs of renal ve ins, w h i c h d ra in b l o o d f r o m t h e k idneys . It a lso rece ives a s ing le pa i r o f geni ta l (ovar ian o r spe rma t i c ) ve ins, w h i c h d ra i n b l o o d f r o m t h e fat bod ies as we l l as f r o m the g o n a d s . Sho r t l y be fo re e n t e r i n g t he s inus venosus , t h e pos te r i o r vena cava a lso rece ives b l o o d f r o m t h e p r o m i n e n t hepat ic veins (pa i red) , w h i c h d ra i n t h e l iver (La t in n a m e , hepar).

3. Renal Portal System

T h e renal po r ta l sys tem is best s t ud ied b e g i n n i n g w i t h t h e sc ia t i c ve in at t h e p lace it was i n j ec ted . T h e sciatic vein (pa i red , as are al l vessels in t h e renal po r ta l sys tem) d ra ins b l o o d f r o m t h e pos te r i o r o r f l e xo r su r face of t h e leg . At t he base of t he t h i g h , a v e n a communicans is f o r m e d be tween t he sc ia t i c a n d f e m o r a l ve ins . M o r e an te r io r l y , t he sc ia t i c and f e m o r a l ve ins j o i n t o f o r m t h e renal portal ve insof e i the r s ide , w h i c h en te r t he s u b s t a n c e of t he k idneys . Jus t an te r io r t o t he u n i o n of t h e sc ia t i c and f e m o r a l ve ins , a dorsolumbar ve in a lso en ters t h e renal po r ta l ve in .

The femora l vein re tu rns b l o o d f r o m t h e an te r i o r o r ex tenso r s ide of t h e leg . It tw i s t s a r o u n d t h e an te r io r s ide of t h e leg , a n d en te rs t h e b o d y cav i ty near t h e i s c h i u m . It g ives off, j us t an te r io r t o t h e vena c o m m u n i c a n s , a pelvic ve in , w h i c h b e l o n g s t o t he hepa t i c por ta l sys tem (see be low) . T h e f e m o r a l ve in t h e n runs an te r io r l y t o j o i n t h e sc ia t i c ve in .

4. Hepatic Portal System

The hepa t i c por ta l sys tem cons i s t s of t w o large ly i n d e p e n d e n t sets of

C i r c u l a t o r y Sys tem 71

vessels : t he ven t ra l a b d o m i n a l ve in (and its t r i bu ta r ies ) , a n d t h e hepa t i c po r ta l ve in (w i th its t r i bu ta r ies ) .

The pelvic veins (pa i red) ar ise f r o m t h e f e m o r a l ve ins j us t an te r i o r t o t h e vena c o m m u n i c a n s . Each pe lv ic ve in rece ives as a t r i bu ta r y a sma l l vesicular vein, d r a i n i n g t he u r ina ry b ladder . T h e t w o pe lv ic ve ins meet each o the r a n d un i te to f o r m the ventra l abdomina l ve in ( unpa i red ) . Th i s p r o m i n e n t ve in w a s observed d u r i n g t he in i t ia l i n s p e c t i o n of t h e v i sce ra ; it r uns a l o n g t h e ven t ra l m id l i ne of t h e b o d y cavi ty . An te r i o r l y , t he ven t ra l a b d o m i n a l ve in sp l i t s i n to r igh t a n d left ha lves, each e n t e r i n g its respec t i ve l obe of t h e l iver. T h e b r a n c h t o t h e left l obe may j o i n w i t h t h e hepa t i c po r ta l ve in be fo re e n t e r i n g t h e l iver. A smal l per icardia l vein ( u n p a i r e d , f l o w i n g pos te r io r l y ) may j o i n t he ven t ra l a b d o m i n a l at or near t h e p o i n t of b r a n c h i n g ; t h i s vessel d r a i n s t h e pe r i ca rd ia l cavi ty a n d t h e hear t m u s c l e .

T h e rema inde r of t h e hepa t i c po r ta l sys tem cons i s t s of t h e hepat ic portal vein a n d its t r i bu ta r i es , al l u n p a i r e d , d r a i n i n g b l o o d f r o m t h e m a j o r d iges t i ve o rgans . T h e ma jo r t r i bu ta r y is t he intest inal ve in , f o r m e d by t h e u n i o n of t h e splenic o r l ienic ve in , d r a i n i n g t he s p l e e n , t h e hemorrhoida l ve ins , d r a i n i n g the la rge in tes t ine a n d c l oaca , a n d t h e mesenter ic ve ins f r o m t h e i l eum of t h e smal l in tes t ine . The in tes t ina l ve in runs an te r io r l y , rece i v ing t w o a d d i t i o n a l t r i bu ta r i es : a duodena l vein f r o m t h e panc reas a n d d u o d e n u m , a n d a cystic vein f r o m the ga l l b ladder . T h e in tes t ina l ve in t h e n m e r g e s w i t h t h e gastr ic vein, f r o m the s t o m a c h , t o f o r m t h e hepa t i c po r ta l ve in . T h e la t ter en te rs t h e s u b s t a n c e of t h e l iver, usua l ly t o g e t h e r w i t h t he left hal f o f t h e ven t ra l a b d o m i n a l ve in .

PALAT0NA8AL

MAXILLARY

OPHTHALMIC

INTERNAL AND EXTERNAL MANDIBULARS

Fig. 31 Arteries of the f rog, ventral view.

72

Fig. 32 Veins of the f rog, ventral view, wi th heart and viscera removed. The tributaries of the hepatic portal vein are shown separately in Fig. 34.

73

74 OPHTHALMIC ORBITONASAL

39-41. MM. PETROHYOIDEI POSTERIORES I. II, AND III \ ! ^ ' " ^ ^ ' -

ATRIA

" C O M M O N CAROTID CAROTID BULB

TRUNCUS ARTERIOSUS

Fig. 33 Arterial circulat ion to the head region, lateral view.

Fig. 34 Hepatic portal c irculat ion. Ventral view, wi th viscera pulled aside.