246 



NATURAL HISTORY. 



SCAPULAR APPARATUS OF 

 TORTOISE. 



One of the peculiarities of the Chelonians is that instead of their shoulder-blade and joint 

 for the arms being outside and iipoii the ribs, as they are in every other group of things 

 possessing ribs and arms, they ai - e beneath the ribs and inside the body. 

 They are under the carapace, which is made up of altered ribs. The 

 shoulder-girdle, of which the shoulder-blade forms, as in the Birds, a very 

 important part, has a coracoid bone of great relittive size, and there 

 is a third large bone connected with the scapula, which is called the 

 acromion process. The girdle is a three-branched structure, and the cavity 

 (glenoid) for the joint of the upper arm -bone is composed of a part of 

 the scapula and part of the coracoid. There is no collar-bone, and as 

 there is no breast-bone or sternum, the shoulder-girdle is hung, as it 

 were, underneath the bodies of the vertebrae. The scapula, which is a 

 cylindrical bone, is directed upwards in the proper position of the animal, 

 and is hung to the body of the second vertebra of the cai'apace by a 

 ligament. The coracoid is flat and more or less triangular, and is directed 

 backwards in the body.* There is nothing like this tripartite incomplete 

 , Scapu^a^o^An-niTi^pfocegBigjj.jjg j n any . o tl ie r order or class of the Vertebrata. 



In the early stage of the existence of the Chelonia the girdle is not 



within the ribs, but in front and outside of them, but during growth the permanent position 

 gradually prevails. This remark applies also to the pelvic bones and part of the thighs, for 

 they, instead of being behind the ribs, are beneath and inside them in adults. 



Everybody who has kept Tortoises, or who has had the opportunity of watching them in a 

 zoological garden, must be struck with the shape of the head as it is slowly put forth from 

 beneath its protecting shell. Its expressionless face, with its large 

 .nose-openings, meaningless eyes, and toothless, lipless jaws, is as 

 remarkable as the apparently large brain-case, which is broad behind 

 and very solid-looking. There is no external ear, but there is a 

 tympanic membrane, which is visible in some kinds. 



To see one of these sedate creatures eating does not give the 

 impression that it is an easy or enjoyable proceeding. The piece 

 of cabbage or other leaf is grasped in the wide gape of the jawp, 

 which have a horny plate instead of teeth, and the motion of the 



lower jaw is simply up and down. The head is projected at each bite, and gradually the 

 morsel is forced down the throat. It is evident, however, that although the creature is very 

 .-slow in its movements it has very good eyes, and that it can detect its favourite food at once. 

 Roaming about slowly, in search of food, the Tortoise turns its head bvit little to the right 

 -or left ; nevertheless, it has the back of the skull well suited for movement, for there is a 

 single condyle, as in the Birds, by which it articulates with the first bone of the vertebral 

 column. 



On comparing the bones of this skull with those of the other classes, it is found that there 

 are no nasal bones present, and that they are i-eplaced by additions to the frontal bones, in the 

 form of two pre-frontals. The parietal bones are largely developed, and are prolonged downwards 

 as thin plates to the bone forming part of the front of the base of the skull or the basi-sphenoid. 

 This prolongation occupies the place of the wing of the sphenoid bone (ali-sphenoid) in Birds. The 

 pre-maxillae are small and are usually united, and the vomer is single and forms a plate below on the 



HEAD OF TURTLE. 



* The bones of the fore-arm joint with a humerus which is remarkable for its shape, which is adapted to support 

 the weight of the body whilst the fore-limb is in movement. When compared with the corresponding bone of a mammal it 

 appears to be out of its axis. The body of the bone is bent, the head of it is very rounded, and there are two knobs or 

 tuberosities near it. One of these is located behind and above and the other is placed inwards and backwards. In the 

 higher animals their position is internal and external, so that the Tortoise's humerus has, as it were, a twist. The lower 

 part of the bone is wide and flat from before backwards, and there is a furrow along the outer border which is especially 

 developed in the marine Chelonians, but less so in the fresh-water kinds, and least in the Tortoises. The marine Chelonians 

 have not the bent condition of the humerus noticed in the land kinds, and the difference relates to their very different 

 mode of life. 



