AVIAN OSTEOLOGY. 399 



process where it occurs in all birds when such an apophysis is 

 present*. 



In the Phalacrocoracidfe, then, the patella is a compound bone, 

 consisting of the true patella posteriorly, and the upper two- 

 thirds, more or less, of the cnemial process of the ti bio-tarsus 

 anteriorly, which latter has become dissociated and thoroughly 

 coossitied with the former. By this union, a foraminal passage 

 is formed for the ambiens muscle, and this, in some species, may 

 gradually, but entirely, disappear, whereupon, in time, the muscle 

 meets its usual fate. 



For very obvious reasons, the patella is very large in Harris's 

 flightless Cormorant (^N annojJterum harrisi) ; indeed, in so far as 

 I have been enabled to discover, it is larger in this species than in 

 any other existing form of the entire family (PI. LXI. figs. 1 &l 2). 

 It has an average height of 25 millimetres, the longest diameter 

 of its base being 19 or 20 millimetres, and is nearly a square in 

 outline. Posteriorly, it is flat and ti-iangular, the acute angle 

 being above. Above its middle, and nearer its posterior surface 

 than its anterior margin, it is pierced, transversely, by the foramen 

 for the ambiens, which is of considerable size. Externally, its 

 exit is almost flush with the surface of the bone, while on the 

 inner aspect it is situated at the base of an extensive concavity. 

 Antei-iorly, this compound bone exhibits a uniform longitudinal 

 excavation which, when the patella is articulated as in life, is the 

 continuation with the similar excavation between the pro- aiid 

 ectocnemial processes of the tibio-tarsus. On the anterior face 

 of this patella, at the lower-internal angle, there is a transvei'se, 

 triangular facet which is intended for articulation with the 

 superior border of the cnemial crest of the tibio-tarsus. In fig. 2 

 we have the mesial or inner aspect of the left patella of 

 iV. harrisi, from the same skeleton (No. 19719), where the 

 perforating foramen for the ambiens is seen at the base of the 

 aforesaid extensive concavity. A study of these two patellfe 

 reveals the nature of the composition of the bone as a whole, as 

 described above. 



Fhalacrocorax penicillatus possesses only a medium - sized 

 patella, which is elongate and wedge-shaped. It has the general 

 form of the patella in Nannopterum : but the transverse fora- 

 minal passage for the ambiens has been entirely absorbed, — not 

 a vestige of it remaining in an individual of the age to which 

 this patella belonged. The union of the two parts composing the 

 bone is very complete, and all traces of their origin have been 

 entirely obliterated, — that is, beyond the anterior rotular channel, 

 and the here extensive facet below it for articulation with the 

 cnemial process of the tibio-tarsus. 



This is a most excellent example of the patella in a Cormorant 



* This is the part referred to by Cones in his 'Key' (5th ed. vol. ii. p. 961), 

 where he describes the patella in the Phalacrocoracidge in the following words : 

 "There is a bulky free patella, coexistent with a short cnemial apophysis or rotular 

 process of tibia, but perfectly distinct therefrom, as in Grebes." It is very evident 

 from this definition that Coues had never given the patella of a Cormorant any very 

 close stud3^ 



