X LIMBS 44 1 



the others three, four, four and three respectively. During the 

 embryonic development the number of phalanges of the fourth 

 and fifth finger increases temporarily, to as many as seven on the 

 fourth, to five or six on the fifth finger. Before the young 

 animal is hatched the numbers are reduced again, chiefly by 

 fusion of adjoining phalanges. This hyperphalangeal condition, 

 typical of Plesiosauri, Ichthyosauri, Cetacea, and several other 

 absolutely aquatic animals, naturally suggests the descent of the 

 present Crocodiles from more essentially aquatic ancestors, but 

 hitherto no trace of supernumerary phalanges has been found in 

 any Jurassic Eusuchia, nor in the Parasuchia and Pseudosuchia. 



The composition of the pelvis is difficult to understand. It 

 consists in the adult stage of three separate bones, of which two 

 only partake in the formation of the acetabulum. The broad 

 ilium sends out two processes ; the posterior and stronger arti- 

 culates with the ischium, which sends out a short and stout 

 process towards the anterior process of the ilium, enclosing a 

 foramen. This process contains a separate centre of ossification, 

 possibly homologous with the true pubis, while each club-shaped 

 bone, loosely attached to it and directed forwards, generally called 

 the pubis of the Crocodiles, would then be equivalent to an 

 epipubis. Neither the " pubes " nor the ischia form a ventral 

 median symphysis. 



The femur is devoid of a prominent inner trochanter. Tibia 

 and fibula are of almost equal strength. The tarsal elements are, 

 in the adult, reduced by fusion to five bones. The fibulare is 

 transformed into a typically projecting, heel-shaped calcaneum, 

 while the intermedium is fused with the tibiale into a broad 

 astragalus. The first, second, and third distal tarsalia are much 

 reduced towards the inner side, and form one w^edge-shaped, partly 

 cartilaginous mass. The fourth tarsale lies between the fibulare 

 and the fourth metatarsal, while the fifth tarsale is hook-shaped 

 and loosely attached to the outer side of the fourth. It has lost 

 its metatarsal and the rest of the fifth finger. Embryos are 

 hyperphalangeal, the fourth toe developing six phalanges, and 

 there are traces of the fifth toe. The numbers are ultimately 

 reduced to 2, 3, 4, 4, on the five toes. The fourth toe remains 

 without a claw. 



Skin. — The epidermal horny layer is not shed periodically nor 

 in pieces ; the wear and tear is made good imperceptibly. The 



