272 AMERICAN TESTUDINATA. Part II. 



The first of these is a very long muscle, originating from the posterior vertebi'a 

 of the trunk, and attached to the foremost neck vertebra and the head. Its 

 function is to draAV back the head and the uppermost part of the neck, so that 

 we may call it musculus retrahens capitis collique superioris. The second muscle 

 is much shorter, originating from the anterior vertebrae of the trunk, and attached 

 to the lower ^^art of the neck. It lies below the first, and its function is to 

 draw the lower jaart of the neck backwards. We may call this muscle M. retrahens 

 colli inferioris. The form into which the neck is thus contracted is that of an 

 S in a vertical plane. I regret deeply that I have not had an opportunity of 

 examining the arrangement of the muscles of those Turtles which bend the neck 

 sideways and fold it under the margin of the shield, as do the Chelyoidge and 

 Hydraspides. 



Considering now the cervical muscles proper, we find a system of shorter 

 muscles largely developed, running from one vertebra to the next or to the 

 next but one. These muscles are particularly subservient to stretching the neck 

 into a straight line, when it has been bent by the muscles described above, and 

 thus to dart it forwards, as all Turtles do more or less rapidly. This action is, 

 however, peculiar and very quick and powerful in the families of Chelydroidaa 

 and Cinosternoida3. 



The posterior part of the dorsal column, with its free vertebrje between the 

 sacrum, the anus, and the tail, is also provided, like the free movable neck, with 

 a well developed muscular aj^paratus, which is jjarticularly powerful in Chelydra. 

 The muscles which move this part originate from the three paii's of pelvic 

 bones. 



The muscles of the shoulder and of the pelvis, which are all inside the bony 

 box, are very difficult to homologize with those which we find in other Reptiles or 

 in other Vertebrata. Two pairs of muscles, originating from the hind part of the 

 plastron and attached to the ossa ischii and pubis, draw the pelvis, the first back- 

 wards, the second forwards. Stannius mentions traces of Musculi recti in some 

 Turtles, originating from the anterior ventral part of the pelvis. Musculi obliqui 

 externi and interni are obvious in almost all Turtles. The obliqui externi are 

 particularly developed. Originating from the inside of the marginal bones of the 

 dermal shield, they are attached to the os pubis. 



The muscles for the shoulder are not much developed in comparison with 

 those of the Saurians or Birds, in which the shoulder lies free on the outside of 

 the ribs. There is one muscle in Turtles drawing the scapula forward, the M. 

 scalenus or levator scapulas of Bojanus, originating from the lower part of the 

 vertebras of the neck and attached to the acromion ; and another, originating from 

 that large crosspiece mentioned above, p. 265, (which may be looked upon as a 



