no Shufeldt, Osteology of Harris's Cormorant. [lif "oci 



In fact, while formed on the same general lines, this sesamoid, 

 composed as described above, with and without a foraminal 

 passage for the ambiens muscle, varies considerably (sometimes) 

 in form throughout the family Phalacrocoracidce generally. 



Returning to the skeleton of Harris's Cormorant, we may say, 

 in regard to its tibio-tarsus (figs. 21, 23. Plate XIX.), that it is a very 

 straight, stout bone, having an average length of some 140 milli- 

 meters. Such part of its cnemial process as remained with the 

 shaft rises well about the summit of the latter, and has well- 

 developed ento- and ecto-cnemial processes. They do not extend 

 far down the front of the shaft, but very soon gradually emerge 

 upon it. Chiefly posteriorly, the level summit extends consider- 

 ably beyond the shaft, and presents on top extensive articular 

 surfaces for the femoral condyles. 



On the outer aspect of the straight, antero-posteriorly flattened 

 shaft there is a very long and wide fibular ridge for the fibula, 

 which latter closely articulates with its entire extent — some 

 30 mm. or more. Anteriorly there is the usual groove in the 

 lower third for the passage of tendons, and this passes under a 

 strong osseous bridge just above the condyles, as we find it in so 

 many birds. Of the two massive condyles, the inner one is much 

 lower on the shaft than the outer, and, combined, they present 

 posteriorly an extensive articular surface for the tarso-metatarsus. 

 A large, free sesamoid is found in the ligaments at the back of 

 the inner condyle, and this is shown in fig. 23 of Plate XIX. I am 

 inclined to think that such a sesamoid does not occur at the back 

 of the outer condyle, as I do not find it in any of the other skeletons 

 where the other is invariably present ; most all, if not all. other 

 Cormorants possess it (P. urile, &c.) 



Some interesting variations are to be found in the tibio-tarsi 

 of other species of this group of birds, as. for example, in the 

 extinct Pallas's Cormorant, the unusually broad fibular crest has 

 its anterior surface in the same plane with the anterior surface 

 of the tibio-tarsal shaft, thus creating a broad, flat area of bone 

 immediately below the cnemial processes. The tendinal canal at 

 the lower end of the shaft is remarkably deep at its lower part, 

 and the osseous bridge spanning it looks, to an unusual degree, 

 upward rather than forward. Throughout the family, however, 

 the morphology of the bone is practically the same, though the 

 study of its variations are highly important. 



In all Cormorants the fihda is remarkably well developed, being 

 long and stout, especially stout opposite the fibular ridge and 

 above, while distally. in some old birds. Harris's Cormorant not 

 excepted, it almost reaches down to the side of the outer 

 condyle of the tibio-tarsus, the short interval being spanned by 

 ligament. 



While the type of them is the same, the tarso-ynetatarsi of Cor- 

 morants likewise exhibit a considerable amount of variation — 

 more so, perhaps, everything else being equal, than do the tibio- 

 tarsi of those birds. In some it is stout and rather shortish ; in 



