Mr. Yarrell on the Anatomy of the Corvorant. 235 



the varying perceptions of the different minds of those engaged in. the 

 pursuit. 



Most of those authors who have written on the comparative anatomy of 

 birds, agree in describing an additional bone as pecuhar to the back part 

 of the head of the Corvorant ; but the muscles attached to this bone, and 

 the services they are destined to render the animal by their united action, 

 have been either overlooked or misconceived. 



Plato VII, figure 1, represents the head of the Corvorant, somewhat 

 reduced in size, with the peculiar bone attached. 



This additional bone is about one inch in length, triangular in shape, 

 somewhat grooved on its surfaces, and from its articulation with the 

 occiput tapers gradually to a point. The mode by which this bone is 

 articulated to the occiput is similar to that observed in the ribs of serpents, 

 in which the condyle is situated upon each vertebra, and the cavity is at 

 the end of the rib ; so in the Corvorant, the condyle is upon the occipital 

 bone, the cavity at the triangular end of the xiphoid bone : the joint is there- 

 fore hemispherical: admitting great extent of motion, the advantages of 

 which will be hearafter pointed out. 



Another subject deserving notice is the great length of the os quadra- 

 turn (letter c, same figure) from above downwards in this bird, and in all 

 others accustomed to feed on fishes. The articulation of this bone both with 

 the cranium itself as well as v/ith the lower mandible admits also great 

 latitude of motion ; it moves with facility backwards, forwards, outwards 

 and inwards by the action of the numerous muscles attached to it, thus 

 increasing the capacity of the pharynx for the more easy pass^e of any 

 unusually large fish that happens to become the prey. 



The plates of bone forming the rami of the lower mandibles in all the 

 species of the genera Coli/mbus, Alca, Uria and Larus are much deeper 

 and thicker in proportion to the size of the different species, than in the 

 Corvorant, in which bird these parts will be found slender, weak and 

 elastic, and hence the value to him of the additional pair of muscles now 

 to be described, and which are not possessed by any of the other birds 

 before mentioned. 



I have before stated that this additional sword-shaped bone in the Cor- 

 vorant has three surfaces each slightly concave, forming together an iso- 

 sceles triangle, the base of which is downwards. From the upper edge 



q2 



