THE SKELETON 45 



dorsal margins. There are three prominences around its periphery, 

 one dorsal arising from the ilium, one antero-ventral formed from 

 the pubis, and one postero-ventral projecting from the ischium. 

 The head of the femur is firmly attached to the two former points 

 by a pair of cotyloid ligaments. 



The Cartilago Tpsiloidea (fig. 36) (Townson, 1795). 



Cart, marsupial ....... Duges (1834). 



Abdominal sternum ..... Sabatier (1880). 



Cart, epipubes . . Wiedersheim, Hoffmann (1876), and others. 



Cart, ypsiloides . . . Hoffmann (1873-8); Whipple (1906). 



As its name implies this is a Y-shaped cartilage lying in the middle 

 line, anterior to the pubo-ischium with which it articulates. It lies 

 dorsal to the M. rectus abdominis and is closely associated with it. 

 As indicated by the synonyms, this cartilage has been homologized 

 with various structures. Whipple (1906) investigated its develop- 

 ment, on a limited supply of material, and concludes that it arises in 

 the linea alba as the result of muscle strain, and has nothing to do 

 with the pelvic girdle. Against the view held by Wiedersheim 

 and Hoffmann that this cartilage is homologous with the epipubis 

 of reptiles, she advances the argument that the cart, ypsiloidea 

 develops and remains entirely dorsal to the rectus muscle, whereas 

 the marsupial bone is ventral to it. 



From observations and experiments on aquatic Salamanders 

 (Diemyctylus) Whipple arrived at the conclusion that, in these 

 forms, the ypsiloid apparatus is definitely correlated with the hydro- 

 static function of the lungs. Thus, by raising the ypsiloid cartilage 

 the animal is able to compress the posterior end of the body cavity 

 and so force the air in the lungs forwards to the anterior end, thus 

 causing the animal's head to rise in the water, while by lowering the 

 cartilage the air is brought back to the posterior end and the head 

 of the animal sinks so that it is able to swim to the bottom. This 

 explanation is of course irrelevant as far as Salamandra is concerned, 

 since this animal is purely terrestrial in the adult stage. Nevertheless 

 it is not unreasonable to suppose that it may be of assistance in 

 defaecation and parturition by virtue of its capacity to compress the 

 posterior abdomen. 



2. The Hind-Limb (Figs. 29-33). 



The form of the hind-limb corresponds with that of the fore-limb 

 except that it bears five digits instead of four. For descriptive pur- 

 poses it may be divided into three regions : {a) the thigh^ containing 



