REPT1LIA. 



275 



draws the head and neck powerfully back- 

 wards; it is the retrahens colli of Bojanus. 

 In the opinion of Cuvier, the former of these 

 two muscles corresponds in function to the 

 sacro lumbalis, and to the transversalis ; the 

 latter to the longissimus dorsi ; but modified in 

 arrangement to suit the disposition of the 

 skeleton. In the turtle they are reduced to 

 a single fasciculus, which runs from the third 

 dorsal vertebra to the basjlar bone, performing 

 the office of the rectus capitis anticus. 



There is a third still more singular muscle 

 which runs along the spine, receiving fibres 

 from all the vertebras, and traversing the in- 

 tervals left between the heads of the ribs and 

 the carapax, and terminating in front upon the 

 anterior surface of the eighth cervical ver- 

 tebra, which it draws forward, and with it 

 the posterior vertical portion of the neck : its 

 position reminds us slightly of the spinalis 

 dorsi, but its insertion is very different. 



A muscular expansion, composed of trans- 

 verse fibres attached on each side to the sides 

 of the vertebrae, envelopes all the lateral and 

 inferior portion of the neck, including the 

 trachea and the oesophagus, joining in front 

 the mylohyoideus, and connecting itself 

 posteriorly with the inner borders of the 

 plastron : this is a cutaneous muscle, similar 

 to that which envelopes the neck of birds. 



In the Chelonian reptiles, the muscles of 

 the head cannot be designated by the same 

 names as those of birds and mammalia, 

 because the carapax gives origin to the 

 greater number of them ; we must therefore 

 content ourselves by indicating their attach- 

 ments. Upon the posterior part of the neck 

 we remark, first, at the anterior edge, to- 

 wards the angle of its crescentic margin, 

 a broad muscle which runs as far as the 

 lateral and posterior parts of the head, where 

 it is inserted : this will draw the head back- 

 wards. 



2d. Beneath, and from the middle of the 

 anterior crescentic space, there arises another 

 muscle,which is slender and round, and which, 

 separating itself from its fellow of the op- 

 posite side, so as to form a figure of V, runs 

 to be inserted upon the external border of 

 the preceding : its office is similar to that 

 of the last. 



3d. The analogue of the splenius capitis 

 arises from the spinous processes of the third, 

 fourth, and fifth vertebras of the neck by 

 distinct slips, and is inserted into the occipital 

 arch : this is the elevator of the head. 



4th. The analogue of the rectus anticus 

 major arises from the inferior tubercles of 

 the four cervical vertebrae which succeed the 

 first, and is inserted fleshy into the basilar 

 fossa beneath the condyle. 



5th. The trachelomastoideus arises from 

 the inferior tubercles of the second and of 

 the third cervical vertebrae, by two thin 

 aponeurotic tendons ; it is inserted thick and 

 fleshy into the eminence which corresponds 

 with the mastoid process : this muscle bends 

 the head to one side. 



6th. Lastly, at the upper part of the 



cervical portion of the spine is a short 

 muscle, which runs from the lower border of 

 the hole formed by the temporal fossae to the 

 spinous apophyses of the first, second, and 

 third cervical vertebrae. 



In front of the neck may be remarked the 

 analogue of the sternomastoideus which 

 arises from the strong aponeuroses which 

 covers the humerus near its articulation with 

 the scapula. Its inferior third only is visible 

 when the skin is raised, the anterior two- 

 thirds being covered by a transverse muscular 

 expansion representing the mylohyoideus, 

 and the platisma myoides. It is inserted 

 underneath the apophysis that corresponds 

 with the mastoid process. Its action will be 

 to draw the head inwards^ and slightly to 

 elevate the shoulder. 



The rectus capitis anticus arises from the 

 inferior spine of the third vertebra of the 

 back, and is inserted by a thin tendon into the 

 basilar process of the occipital bone. 



In the Chelonian reptiles the head is arti- 

 culated with the atlas by means of a single 

 condyle ; in the land^tortoises it is prolonged 

 and divided into two ; in the turtles it pre- 

 sents three articulating surfaces resembling 

 the leaf of trefoil. As this tubercle penetrates 

 very deeply into the corresponding cavitv of 

 the atlas, the lateral movements of the head 

 must be extremely limited ; the other move- 

 ments of the head in the Chelonians are those 

 of protraction and retraction : these depend 

 upon the flexion and extension of the neck. 



In the Trionyx, Nature has doubly provided 

 against any lateral movement in the posterior 

 region of the neck ; first, the articulations of 

 the last cervical vertebra with the first dorsal 

 are disposed so as to form an angular hinge, 

 the posterior articular apophyses of the cer- 

 vical forming a hollow cylinder, whilst the 

 anterior articulating process of the dorsal is 

 likewise cylindrical ; secondly, the body of 

 the eighth cervical terminates anteriorly in 

 two condyles, which are received in corre- 

 sponding cavities in the body of the seventh. 



In the Matamata, which, instead of bending 

 its neck vertically, bends it by lateral flexion, 

 the disposition of the articulations is entirely 

 different. The body of the eighth cervical ver- 

 tebra is compressecl laterally, and rounded at 

 each end ; that of the seventh, on the con- 

 trary, is excavated at both extremities ; that 

 of the sixth rounded posteriorly, and hollowed 

 in front ; the fifth rounded at both ends ; and 

 the others, as usual, concave posteriorly and 

 convex before. 



It results from this arrangement, combined 

 with the disposition of the articular apo- 

 physes, that the neck is capable of a double 

 lateral curvature. 



Muscles of the Shoulder. These muscles 

 in the Chelonian reptiles differ considerably 

 from those of other vertebrate animals : they 

 are four in number. 



The first is attached beneath the edge of 

 the carapax between the two ribs, and the 

 pieces usually regarded as sternal ribs, from 

 the second to the fifth. It is very thin, and 



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