iqi5 



^^ 1 SnvFKi.vT, Osieoloi^y of Harris's Cormurant. lOQ 



In Cormorants something entirely different i'rom eitlu.i- the 

 Grebes or the Loons obtains, and what I find to be the case 1 think 

 will hold thronghout the Fhalacrocoracidce. In this family, the 

 upper or proximal half of the cnemial process of the tibio-tarsus 

 has, in the young, become dissociated entirely, and in the adult, 

 as a free segment, eventually completely co-ossifies with the big 

 true patella forming the aforesaid sesamoid, which heretofore has 

 always been described as the patella, irrespective of the fact that 

 its entire anterior third is re])resented by the proximal moiety 

 of the cnemial process of the tibio-tarsus. In many birds the 

 ambiens muscle has a groove for its accommodation on the anterior 

 face of the patella, and this was probably the case in the ancestors 

 of tlie Cormorants, jjiior to the time when, for some reason or 

 other, the upper half of the cnemial process of the tibio-tarsus 

 becomes dissociated and thoroughly fused with the true patella 

 behind it. When this came about, the ambiens muscle, which 

 originally passed in a groove on the anterior face of the patella, 

 came to j)ass through a foramen, which foraminal passage was 

 formed in the manner above pointed out. 



In some Cormorants this foraminal passsage is extremely 

 minute, and I believe that in such species it will be found that 

 the ambiens muscle is gradually disappearing This is the case in 

 a skeleton of P urile before me (No. 19,655, Coll. U.S. Nat. Mus.), 

 where the line of union or fusion of the patella, and the dis- 

 sociated upper half of the cnemial apophysis of the tibio-tarsus 

 can be most plainly discerned. All this is still more evident in 

 the patella of P. auritus {"P. dilophiis") (No. 19,262, Coll. U.S. 

 Nat. Mus.), where the ambiens not only goes through the fora- 

 minal passage aforesaid, but the entire dissociated cnemial 

 apophysial portion can be made out. Indeed, the apex of the 

 latter is distinct from the apex of the patella. 



In P. vigua this compound patella is comparatively small, and 

 its compound nature, as described above, very distinct, the 

 passage for the ambiens being commodious. 



In P. carbo (No. 18.851, Coll. U.S. Nat. Mus.) the foraminal 

 passage for the ambiens is almost entirely absorbed in both 

 patellae, while the part of the cnemial apophysis which has united 

 with the patella, as in the other Cormorants above described, is 

 most clearly to be made out 



The foraminal passage has entirely dsappeared in P. penicillatus, 

 and the patella is wedge-shaped and longer longitudinally than 

 in other Cormorants. The part of the tibio-tarsal cnemial process, 

 which has united with it to form the big, free sesamoid, is plainly 

 to be made out. 



P. albiventris has the foraminal passage nearly gone — impervious 

 in some individuals — and the bone clearly showing its composition. 



insertion, and probably the true patella has co-ossilicd in the adult with 

 the elongated cnemial process of the tibio-tarsus." In this matter, then, 

 as stated above, two groups of divers are, morjiholot^ically, cpiite dis- 

 similar. 



