282 



REPTILIA. 



middle of its length. This muscle is described 

 by Sir Everard Home* as being in the boa 

 constrictor divided into two, an upper and a 

 lower portion ; but in other species, although 

 a slight line of demarcation may be detected, 

 such a division is scarcely admissible. 



From the ribs of serpents muscular fasci- 



Fig. 203. 



An internal View of the Muscles which move the Ribs 

 in the Boa Constrictor. 



A A, the muscles which pass from cartilage to 

 cartilage of the different ribs ; B B, a set of muscles 

 which pass from the point of each rib, over two 

 ribs to the middle of the third ; c, a similar set of 

 muscles continued from the opposite side of the rib, 

 passing over three ribs to the body of the vertebra ; 

 DD, the abdominal muscles which arise from the 

 anterior edge of each rib, and pass to the linea alba ; 

 E, the linea alba; FF, the terminations of the 

 oblique muscles which pass from the bony ex- 

 tremities of the ribs to the edges of the scuta; GO, 

 the muscles of the scuta, consisting of two sets, 

 which decussate each other. 



culi are given off, which go to be inserted 

 into the skin : some of these arise from the 

 same point as the great lateral costals. Their 

 course is from before backwards, and from 

 above downwards as they run, spreading out 

 like a fan, to be attached to the sides of the 

 ventral scuta. The others arise from the 

 lower part of the rib, opposite the point 

 of attachment of the long inferior costal 

 muscle ; these run from behind forwards to be 

 fixed to the angle of a ventral scutum, about 



* Lectures on Comp. Anat., vol. i. 



three ribs off. The ribs, moreover, give at- 

 tachment to a visceral muscle. 



In serpents there is only one muscle pro- 

 per to the head, which seems to represent 

 the complexus ; this arises from the articular 

 apophyses of the five or six anterior vertebrae, 

 and is inserted into the mastoid bone. 



The transverso-spinalis is continued as far 

 forwards as the occipital bone, and thus re- 

 places the recti capitis. The movements of 

 the head upon the spine are, indeed, very 

 limited in the ophidia. The body of the 

 atlas presents three articular facets arranged 

 after the manner of the leaves of a trefoil, 

 which are attached to the occiput beneath 

 the foramen magnum, so that the head is not 

 more moveable upon the atlas than the other 

 vertebrae upon each other. 



The muscles of the head of serpents have 

 been carefully dissected by M. Duges*, M. 

 Duvernoyf, Brandt and RatzburgJ, and 

 others. The following brief account of this 

 part of their myology, taken from the last 

 edition of Cuvier's Anatomic Comparee, must, 

 however, suffice for our present purpose. 



The true serpents have the zygomatic 

 (tympanic) bones (fig. 205, 7) moveable, 

 and suspended from another bone analogous 

 to the mastoid (6), which is attached to the 

 cranium by means of muscles and ligaments that 

 allow of considerable mobility : the two sides 

 of the lower jaw, moreover, are but loosely 

 connected with each other, and the superior 

 maxillary bones (2) are only united to the 

 inter- maxillary bones (1) by ligaments, so 

 that they can be separated to a greater or 

 less extent ; a circumstance which confers 

 upon these reptiles the faculty of dilating 

 their rictus, thus enabling them to swallow 

 animals whole which could not otherwise by 

 possibility pass into their mouths. In ad- 

 dition to the above arrangement, the maxil- 

 laries (2), the palatine bones, and the ossa 

 pterygoidea (3, 4), are more or less moveable 

 beneath the cranium, so that the animal can 

 raise or depress the palatine or pterygoid 

 arches, as well as those formed by the upper 

 maxilla, and also can separate them, or ap- 

 proximate them to each other. 



The muscles subservient to the movements 

 of the jaws are the following : 



All serpents whose mandibular arches are 

 moveable, as above described, have generally 

 three distinct temporal muscles, one anterior, 

 one median, and the other posterior. 



The anterior temporal (fig. 204, e] is at- 

 tached superiorly behind the orbit, and de- 

 scending downwards and backwards, winds 

 round the commissure of the lips, and turning 

 forward again (e'\ is inserted into the lower 

 jaw, very considerably in front of the angle 

 of the mouth. 



The middle temporal (fig. 204, i.} is partly 

 covered by the anterior temporal, it descends 

 nearly vertically from the middle and upper 



* Ann. des Sc. Nat. torn. xii. 1827. p. 378. 

 t Ann. des Sc. Nat. torn. xxvi. 1832. p. 113. 

 j Medezinische Zoologie, 4to. 1829 



