CHAPTER V I

STRUCTURE AND DISPOSITION O F THE LOCOMOTORY MUSCLES

Of the four classes of land vertebrates, Amphibians and

Reptiles have limbless representatives. In snakes the lack of

appendages presents certain basic myological changes which involve

the development of increased complexity in musculature and allowing

greater variety of movements.

The main groups of body muscles important in locomotion

are muscles between vertebrae, between vertebrae and ribs, between

ribs and the ribs or vertbrae to the integument. The musculature of

the snake body is formed by the repeatition of muscles throughout its

length. Mosauer (1935) attempted to construct a phylogeny of snakes

based on the interspecific variation of body muscles. Gasc (1967)

described the axial musculature of lizards and snakes. Ruben (1977)

briefly dealt with the correlations between locomotion and axial

musculature in Lichanura and Masticophis. Bhati and Dutta (1977)

described the trunk musculature of Ptyas nlucosus.

Despite of all these studies. much remains to be learned

regarding the functional anatomy and loconiotor ability in snakes. This

study is important to understand the structural and functional

demands placed on efficient locomotory system of Eryx conlcus,

Dyophis nasutus and Deridrelapllis tristis.

The nomenclature of the locon~otory muscles followed in this

is that of Bhati and Dutta (1977)

The following is an account of tlie structure and disposition

of the locomotory n~uscles of the snaltes in tlie present study. The

relative length of muscles and snout vent length (SVL] are

summarised in Table 6.1

M. spinalis (Fig. 6.1, 6.2 & 6.3)

M.spinalis is a parallel-fibred muscle which orginates

tendinously from the lateral side of the neural spine. The muscle

extends forwards by the lateral sides of the neural spines. It fuses

together anteriorly with M.semispinalis preceding the third vertebrae

and extends forwards a s a single muscle. In D. nasutus and D. tristis,

this muscle runs over thirty four vertebrae where it gets inserted

tendinously on the clorso-lateral surface of the anterior part of the

neural spine. The bt:lly of the muscle covers four vertebrae. In E.

conicus, it arises by a flat, very short tendon and runs over thirteen

vertebrae and attaches tendinously on the fourteenth vertebra.

The relaltive length of M.spinalis and snout vent length

shows marked variation between the three snakes. This is 20.55% in

D. trlstis. In E. corlicus and D. nasutus, it is 7.10% and 16.94%

respectively.

M.semispinalis (Fig. 6.1, 6.2 & 6.3)

M.semispir~alis is a parallel fibred muscle which originates

from the lateral side of neural spine of each vertebra except atlas and

axis. In D. rlusutus and D. tristis. this muscle fuse together with

M.spinalis in the region of the preceding third vertebra, from its

origin and extends forwards as a single n~uscle. The common tendon

gradually tapers anti inserts on the dorso-lateral surface of the

anterior part of the neural spine of the preceding thirty fourth

vertebra. In E. corticus there is no marked separation between these

muscles. They fuse together and function as a single muscle.

The relative length of M. spinalis and snout vent length

ranges from a maximum of 22.83% in D. tristis to a minimum of

7.14% i11 E. corlicus. It is 18.39% in D. itasutus.

M.longissirnus dorsi (Fig. 6.1, 6.2 & 6.3)

M. longissimus dorsi is an elongated flat, parallel Bbred

muscle with tendinous orgin from the cranio-lateral portion of the

prezygapophysis. 111 E. conicus, it extends forwards and is tendinously

inserted on the preceding sixth vertebra. In D. rlasutus and D. tristis.

it extends forwards along with the M.i~lterarticularis inferior. At the

level of the nineth vertebra, it divides into dorsal and ventral part.

The dorsal part extends upwards and forwards. and tendinously

inserts at the base of the neural spine. The tendon of the ventral

part extends forwards and downwards, and is inserted on the tenth

vertebra on the posterior face by a thin tendon.

The relative length of M. longiss i~~~us dorsi and snout vent

length is 6.33% in D. tristis. 3.5% in E. coriicus and 5.69% in D.

nasutus.

M.multifidus (Fig. 6.1, 6.2 & 6.3)

The M. muitifidus originates fro111 the neural arches, a little

behind the orgin of the Mspinalis, by a flat tendon. It extends along

the inner surface of the M.spinalis up to the fourth segment. where

the fibres get inserted on the posterior border of the neural spine of

the preceding vertebra, just above the postzygapophysis. The muscles

orginating from the anteriormost four vertebrae are inserted by a

common flat tendon on the posterior surface of the basisphenoid

bone. In E. coriicus, this muscle spans over three vertebrae and in D.

nasutus and D. tristis it spreads over four vertebrae.

The relative length of M.multifidus and snout vent length is

Figure 6.1

Figure 6.1

Locomorory rliuscles of E q x conicus

6.1 (a ) Lateral view of the musculature of the middle thoracic

region !seriii-digra~~lmaric)

6.1 (b) \ 'rntral view of the n~i~scu la ture of t he ventral body

wall (st-11:i-digranlniatic)

Abbreviatioris

Ms - hl ~1>111:tlis: h 1 5 j ~ - se~iiipi~ialis;

Mid - h? i ~ ~ i i g i s ~ i m u s dorsi: hlri) - multifidus:

Mis - M, interai-ticularis superior:

h i - h . int~rarticularis inferior: Mi - hl. intervertebralis;

Mrc - h1. retractor costae biceps:

Mlc - hl, levator costae: hlt - M. tuberculocostalis:

Mtd - hl . tralls\:ersus dursalis;

Mcis - hl.costalis internus superior:

Mcii - h.1. costalis internus inferior;

Mcv - hl. costovt.rtebrucosralis:

Mip - hl intrriostalis pi-oprius:

Mra - hl, rec'lus ?Ibd~~lllilliS:

Mta - hl. transversus abdominis:

Msd - M , suy~racostalis dorsalis:

Mcs - M . costocutaneous superior;

Mci - M . costocutaneous inferior.

Mcv

I

2.26% in E. corricus. This is 2.16% in D. nasutus and 2.48% in D.

tristis.

M.interarticularis superior (Fig. 6.1, 6.2 & 6.3)

M.interarticularis superior is a short, parallel-fibred muscle.

which orginates tcndinously from the dorsal surface of the

postzygapophysis and extends forwards on the lateral surface of the

M.spinalis. I t is inserted tendinously on the posterior edge of the

postzygapophysis of the preceding vertebra. It further runs forwards a s

a thin muscular slip which is inserted on the prezygapophysis of the

same vertebra. The disposition of this muscle is more or less same in

the three snakes.

The relative length of M.interarticularis superior and snout

vent length in E. corlicus, D. rlasutus and D. tristis is 1.46%. 0.84%

and 1.2 1% respectively.

M.interarticularis inferior (Fig. 6.1, 6.2 & 6.3)

The M.interarticularis inferior is a parallel-fibred muscle. I t

has tendinous orgin from the prezygapophysis. During its course, it

lies concealed by the M.longissimus dorsi. 111 E. conicus, it is

originated from the prezygapophysis and is inserted by short tendon

on the prezygaphysis of the preceding fourth vertebra. In D. nasutus

and D. tristis, it is inserted by a tendon on the fifth vertebra.

The relative length of M.interarticularis inferior and snout

vent length is 3.09% in E. cor~icus and 2.21% in D. nasutus. I t is

2.88% 111 D. tristis.

M.intervertebralis (Fig. 6.1, 6.2 & 6.3)

M.intervertebralis is a short, parallel fibred muscle which

connects the succeeding vertebra to each other. I t h a s fleshy origin

from the lateral part of the neural arch and is fleshly inserted on the

postero-lateral side of the neural arch of the preceding vertebra. The

arrangement is same in the three snaltes. The relative length of

M.interarticularis in E. conicus. D. nasutus and D. tristis is 0.64%,

0.49% and 0.57% ~.espectively.

M.retractor costae biceps (Fig. 6.1, 6.2 & 6.3)

M.retractor costae biceps consists of two fleshy bellies, in

each segment which are joined by an aponeurosis. The median belly

arises by continuation of the M.longissimus dorsi. The lateral belly is

like the median one. but originates from an intermediate aponeurosis.

In E. conicus, it is originated by a short tendon, extends forewards

and is tentiinously inserted on the inner side of the nineth rib. In D.

nasutus, it is inserted on the fourteenth rib. In D. tristis, it spans

over fifteen ribs and is inserted on the innerside of the sixteenth rib.

In D. nasutus atid D. tristis anterior tendon of this muscle is long.

This muscle shows marked variation among the three species.

Figure 6.2

Figure 6.2

Locomotfiry nlusclrs of Dryophis nasutus

6.2 ( a ) L;iteral view o f the m~~sc~u ln tu re of rlle lniddle thoracic

region (semi-digrammatic]

6.2 (b ) Ventral view of the ~nusculature of the ventral body

wall (senti-diagra.mmatid

Abbreviations:

Ms - h:.sj~inrilis: Msp - M. se~~iispinalis :

Mld - h l , loiigissiinus dorsi: &I111 - M. multifidus:

Mis - hl. interarticularis superior:

Mii - h1. interal-ticularis inferior: M i - hl. intervertebralis:

Mrc - hl. retractor costae biceps:

I - I Irvatar costa?:

M t - h1 t~~t i r rc~~locos tn l i s :

Mtd - kt. transvcrsus (101-salis:

Mcis - hl. costalis iilternus superior;

Mcii - hl. costalis illternus inferior;

Mcv - h l , costovertebl-ocostalis:

I - 1 intercostalis proprius:

Mra - 31, rcctus abdoi~liiiis;

M t a - hl. transversus abdomi~iis;

Msd - M . supracostalis dorsalis:

Mcs - M . costocutaneous superior:

Mci - M, costucutaneous inferior.

(a) M r l s M c v Mfd I

I Mra

I Figure 6.2 M C I I

The relative: length of M.retractor costae biceps and snout

vent length is 7.07% in D. nasutus and 6.01% in E. conicus. It is

9.58% in D. tristis.

M.levator costae (Fig. 6.1, 6.2 & 6.3)

M.levator costae is a parallel-fibred, short muscle which

tendinously arises froln the posterior ventral surface of the

prezygapophysis. It extends posteriorwards and downwards, which is

tendinously inserted on the dorsal side of the rib of the succeeding

vertebra. During its course, it covers M.tuberculocostalis,

M.costovertebrocostalis and M.intercostalis proprius. In E. conicus, it is

broad and massive than the other two snaltes. The disposition is

similar in the three snaltes.

The relative length of M.levator costae and snout vent length

in E. conicus. D. nusutus and D. tristis is 1.57%. 1.08% and 1.32%

respectively.

M.tuberculocostalis (Fig. 6.1, 6.2 & 6.3)

M.tuberculocostalis is a short, parallel-fibred muscle. I t

orginates from the posterior surface of the capitulum of the rib by a

short tendon and extends bacltwards between the

M.costovertebrocosalis and M.levator costae. After spanning one

segment, it gets fleshy insertion below the capitulum on the

antero-dorsal surface of the rib of the succeeding vertebra. This

muscle has the same arrangement in the three snakes.

The relative length of M.tuberculocostalis and snout vent

length varies from 1.09% in E. conicus to 1.22% in D. nasutus. In D.

tristis it is 1.16%.

M.transversus dorsalis (Fig. 6.1, 6.2 & 6.3)

M.transversus dorsalis is a deep seated slender muscle lying

between the proxim;%l end of the succeeding rib. It arises fleshly from

the ventral median crest of the vertebral column, and forms a

muscular sheath. The muscle extends forwards and downwards, and

is inserted fleshly on the second preceding rib on its medial side. The

structure and disposition is same in the three snakes.

The' relative length of M.transversus dorsalis and snout vent

length in E. conicus. D. rtasutus and D. tristis is 1.66%, 0.79% and

1.07% respectively.

M.costalis internus superior (Fig. 6.1, 6.2 & 6.3)

M.costalis internus superior has the same origin as that of

M.transversus dorsalis. This muscle together form the muscular lining

of the body. In D. r~asu tus and D. tristis, this muscle spans obliquely

forwards and is fleshly inserted on the posterio-lateral surface of the

preceding third rib. It is covered ventrally by M.transversus dorsalis,

Figure 6.3

Figure 6.3

Locomotury muscles of Der~drelaphis tristis

6.3 (a) Lateral view of the m ~ ~ s c ~ r l a t u r e of the middle thoracic

region (sr111i-diagrammatic)

6.3 ( b ) L'entral view of the rn~isculature of the ventral body

wall [ se~ni-diagranl~~~at ic ' )

Abbreviatiolis

Ms. M. s i~inal is ; hlsp - h1. sel~iispinalis:

Mld - h l l u ~ r g i s s i n i ~ ~ s ci:rr.;i: R.lrli - M. n1ultifidus:

hlis - hZ. irlrerarticularis superior.

Mii - M . i~lterarticuleris inferiur:

Mi - hl i l l t e~~er tebra l i s :

Mrc - hl retractor costa? biceps:

Mlc - hl, levatol: costae: hlt - hl. tuberculocostalis:

Mtd - hI t ra~is \ : r rsus dorsalis:

Mcis - hl. costalis in t r rnus s u ~ ~ r r i o r ;

Mcii - hl. costa1.i~ i r l t ~ r n u s iilfrl~ror:

Mc\' - hl. costo\:ei-tebr-ocostalis:

Mip - hl. inter-costalis proprius:

Mra - M. rectils abdominis:

Mta - M , trans\ 'ersus abdominis:

Msd - M . supracostalis dorsalis;

Mcs - M. costocuta~reous superior;

Mci - hl. costocutaneous inferior.

1 Mlc Mia MCS MCI ~ b d

M t d Mcv I

Figure 6.3 I I

Mra M c l l I M P

and dorsally by M.cc~stovertebrocostalis and M.costalis internus inferior.

In E. conicus, it is inserted on the postero-lateral surface of the

preceding seventh rill.

The relative length of M.costalis internus superior and snout

vent length is greatest in E. conicus. It is ranges from a minimum of

1.37% in I3). r l a s u t ~ ~ s to a maximum of 4.12% in E. conicus. It is

1.79% in 13. tristis.

M.costalis internus inferior (Fig. 6.1, 6.2 & 6.3)

M. costalis internus inferior is tendinously originated from the

ventral side of the centrum, close to the origin of M. costalis internus

superior. It extends bacltwards, below the M. costalis internus superior

and skips over two segments. It is fleshly inserted on the distal end

of the third rib. The arrangement of muscle fibres is of similar

pattern in the three snakes.

The relative length of M.costocutaneous inferior and snout

vent length in D. r,~asutus is l.OS%. 1.33% in D. tristis and 1.64% in

E. conicus.

M.costovertebrocostalis (Fig. 6.1, 6.2 & 6.3)

M.costovertebrocosta1is is a small, broad muscle which covers

the ventro-lateral surface of the vertebra and extends backwards. It is

fleshly inserted on the proximal part of the succeeding rib. During its

course it is covered ventrally by M.costalis internus superior and

dorsally by M.levato1- costae and M.tuberculocostalis. The disposition of

this muscle is more or less same in the three snakes.

In E, coriicus, the relative length of M. costovertebrocostalis

and snout vent length is 1.28%. In D. r~asutus and D. tristis it is

0.71% and 0.87% respectively.

M.intercostalis proprius (Fig. 6.1, 6.2 & 6.3)

M.intercostalis proprius is a thin muscular sheath which

occupies the space between the successive ribs. It fleshly orginates

from the posterior surface of the rib and extends backwards. This

muscle is inserted fleshly on the anterior surface of the following rib.

It is covered dorsa1l:y by M.levator costae, M.supracostalis dorsalis and

M.costocutaneous superior. The disposition of M. intercostalis proprius

is same in the three snakes.

There is no marked variation in the relative length of

M.intercostalis proprius and snout vent length in the three snakes.

M.rectus abdominis (Fig. 6.1, 6.2 8( 6.3)

M.rectus abdominis is lying between the bony extremities of

the successive ribs. It is fleshly orginated from the posterior surface

of the rib and is inserted fleshly on the anterior surface of the

following r i b The disposition of this muscle is more or less same in

the three snakes.

The relativt. length of M.rectus abdominis and snout vent

length is 0.72% in D. r~osutus. It is 0.72% in E. cortlcus and 0.68%

in D. tristis.

M.transversus abdominis (Fig. 6.1, 6.2 & 6.3)

M.transversus abdominis forms the innermost layer of the

body wall. It fleshly arises from the ribs, extends slightly downwards

a n d backwards. T h ~ s muscle fleshly insert to the integument in the

mid ventral line. The slips join to form a thin muscular sheath. The

disposition is similar in the three snalces.

The relative length of M.transversus abdominis and snout

vent length in E. c ' o ~ ~ i c ~ l s is 2.4%, 1.23% in D. rlasutus and 1.24% in

D. tristis.

M.supracostalis dorsalis (Fig. 6.1, 6.2 & 6.3)

M.supracostalis dorsalis is a n elongated flat muscle which

originates by a short tendon from the inner surface of the proximal

part of the rib, close to the i~lsertion of the M.retractor costae biceps.

In E. cor~icus, this muscle extends baclcwards and downwards,

gradually becomes broader, and is inserted after spanning seven

segments on the anterior surface a t the distal end of the eighth rib.

In D. nasutcls a ~ i d 1). tristis, after spanning four segments, tendinously

inserted on the distal end of the fifth rib.

The relative length of M. supracostalis dorsalis and snout

vent length 1s 4.80% in E. corticus. In D. riasutus and D. tristis this

is 2.42% and 3.04% respectively.

M.costocutaneous superior (Fig. 6.1, 6.2 & 6.3)

M.costocutaneous superior is an elongated, parallel - flbred

muscle. It originates, by a short tendon from the proximal part of the

rib. This muscle runs bacltwards laterally and covers seven ribs. I t

fleshly inserted to the dorsal s ~ ~ r f a c e of the integument. In E. conicus,

this musclr is broader and in D. nasutus and I: D. tristis it is

narrow and thin.

The relative length of M. costocutaneous superior and snout

vent length shows marked variation. In E. corticus,D. nasutus and D.

tristis, this value is 5.43%, 3.51% and 4.58% respectively.

M. costocutaneous inferior (Fig. 6.1, 6.2 & 6.3)

M.costocutaneous inferior is a slender, parallel-fibred muscle

which fleshly orginates from the lateral surface of the cartilaginous

part of the rib. In E. conicus, it extends forwards and after spanning

four segml-nts, is fleshly inserted on the dorsal surface of the

integument. In D. r~asutus and D. tristis,i!>. this muscle runs forwards

and after spanning two ribs, it is insertcd on the dorsal surface of

the integument.

The relative length of M.costocutaneous inferior and snout

vent length shows n-larked variation. In E. conicus it is 3.00% and in

D. nasutus and D. tr-istis it is 1.40% and 1.78% respectively.

Muscle length and snout vent length ratio

The percent.age of muscle length and snout vent length are

summarised in Table 6.1. M.spinalis and M.semispinalis show marked

variation between the three snaltes. It ranges from a maximum of

18.39 cm in D. nasi~tus to a minimum of 3.9 cm in E. conicus. In D.

tristis it measures 15.90 cm. But the relative length of the muscle

and snout length is highest in Denrelaphis (22.83%). In E. conicus

and D. nasutus it is 7.14% and 18.39% respectively. Among the other

epaxial muscles; M.m~~ltifidus, M.interarticularis superior and

M.interarticularis inferior, have no marlted variation in length of each

species. M.longissirnus dorsi shows difference between the three

species. It measures 3.50 cm in E. conicus and 5.80 cm in Dyrophls.

In D. tristis this measures 4.41 cm M. intervertebralis is the shortest

muscle (Table 6.1) which has more or less same length in the three

species, ie. 0.33cm in E. cor~cius. 0.50cm in D. nasutus and 0.40cm

in D. tristis.

TABLE VI. I. Length of muscle (ML) and snout vent length (SVL)

percentage of Eryx conicus, Dryophis nasutus and

Dendrelaphis tristis.

M ~ ~ s c l e

M.Multifidus 1.24 r 0 . ~ 0 2.26 2.20 s 0.26 2.16 1.73 + 0.12 2.48 -

M.lnterarticularis 0.80 r 0 . 1 1 1.46 0.01 * 0.13 0.61 0.84 +0 .10 1.21 superior

M.Interarticularis 1.70 r 0.23 3.09 2.25 r 0.26 2.21 2.01 + 0.26 2.88 inferior

M.lntervertebl-alis 0.35 * 0.05 0.64 0.50 r ,070 0.40 0.40 -0 .40 0.57 I

M.Retractor 3 . 3 V r O l S 6.01 7 . 2 2 r 0 . 3 8 7.07 6 . 6 7 ~ 0 . 2 4 0.58 cos taeb ice l~s ---- M.Levator costae IF 1.57 j 1.10 = 0.12 1.06 0.02 ~ 0 . 0 7 1.32

I

M.Tuberculocostalis

M.Transversus dorsalis --

M.Costalis internus superior

M.Costalis i ~ i t c r n u s inferior

M.Costovertebi-ocosta lis

M.lntercostalis proprills

-.

M.Rectus ahdurr~ir~is --- M.Transversus

abdomins

M.Spupracostalis dorsalis

M . C o s t o c ~ ~ t a ~ i r o u s supel-ior

--

M . C o s t o c ~ ~ t a r ~ e o u s inferior - -

X = Mean, S.D. = S t a n d a r d d e v i a t i o n

Anlong the hypaxial muscles. M.retractor costae biceps.

M.costalis internus superior. M.transversus abdominis. M.supracostalis

dorsalis. M.costocut;~neous superior and M.costocutaneous inferior show

high segmental length ('Table 6.1) than other hypaxlal muscles in these

snakes. The M.retractor costae biceps is longer than other hypaxial

muscles in the snakes studied. In E. conicus. M.costalis internus superor.

M. transvers u s abdominis, M .supracostalis dorsalis. M. costocutaneous

superior and M. costocutalleous inferior have higher muscle length and

snout vent length ratio than D. rlasutus and D. tristis. M. intercostalis

proprius and M. rectus abtlominis have least linear measureme~lt (Table

6.1) among hypaxial ~ n ~ l s l e s of these three snakes. This measures 0.40cm

in E. conicus. 0.Glcm in D. rtasutus and 0.4Scm in D. tristis.