142 REPTILIA. 



number, are always freely moveable, and to such a degree in the 

 Land and Fresh-water Tortoises, that the neck can be retracted be- 

 neath the carapace. They are similar to those of the Lizards, 

 and provided with long but very depressed superior and inferior 

 spinous processes. The odontoid process of the second cervical 

 vertebra is constituted by a distinct bone. The two sacral, as also 

 the caudal vertebrae, few in number, are provided with strong 

 transverse processes. The bodies of the dorsal vertebrae are of 

 very peculiar construction, being very long and narrow, and anchy- 

 losed to the dorsal shield, and hollowed out superiorly for the lodge- 

 ment of the spinal cord. By making a perpendicular section of 

 young specimens, the bodies may be readily perceived with the 

 arches alternating with them. A distinct series of bones of a 

 flattened form may at the same time be seen in the upper part of 

 the section, to be situated upon the spinous processes ; they form 

 the middle row of dorsal scutes, and are partially anchylosed 

 together, and with the ribs, by suture. They belong to the dermo- 

 skeleton, and in adult animals coalesce completely with the spinous 

 processes. The lateral parts of the carapace also consist of anchy- 

 losed ribs and dermal bones. In young specimens the ribs are s^en 

 to be narrow, and are plainly distinguishable from the dermal bones. 

 The origin of the rib, or its narrow neck, may be also detected, and 

 the mode by which the head uniting with the bodies of two verte- 

 brae, and also with their arches, forms the tubercvlum cost. In 

 adult specimens of the Land Tortoises, the tegumentary bones are 

 so strongly anchylosed together, that the two ribs which were 

 originally distinct, become completely absorbed, and even the costal 

 necks and heads are represented by only thin bony fibres. Ex- 

 ternally the carapace is surrounded by a circle of quadrangular, or 

 elongated bony scutes, which belong entirely to the tegumentary 

 skeleton, and replace as it were, the costal-cartilages, while they are 

 in part firmly united to the plastron. This union is effected more- 

 over by means of a sternum, and several dermal bones anchylosed 

 to it, as may be also seen in young specimens. The plastron con- 

 sists of eight pieces united by suture, or by fibro-cartilage, and of a 

 single piece intercalated between the four anterior ones, and which 

 may be regarded as a kind of manubrium sterni. In the Land and 

 River Tortoises, at least in Emys, this piece consists of a large and 

 entire plate ; in Trionyx, and the Marine Tortoises (e. g. Chelonia), 

 it is perforated by irregular apertures, and the anterior pieces con- 

 cur to form a T-shaped bone, which reminds us of the structure of 



