REPORT ON THE SPHENISCID^. 137 



cartilage, close to the posterior border of the latter. The fibres converge as they pass 

 forwards, and are inserted into the basi-hyal, into the uro-hyal, and to a small extent into 

 the base of the apo-hyal bone. 



Action. — The thyro-hyoid muscle approximates the larynx to the hyoid bone. 



Relations. — This muscle is separated from its fellow by the uro-hyal cartilage. Its 

 origin corresponds to the insertion of the contractor-tracheae muscle. 



Nerve supply (?) 



Concluding Observations. 



A consideration of the facts above detailed regarding the muscular system of the 

 Spheniscidse, leads to the conclusion that so far as theix muscular system is concerned, 

 these birds constitute a clearly defined group of the Palmipedes. Agreeing essentially 

 with that of the order just named, the muscular system of the Spheniscidse nevertheless 

 presents certain modifications which, occurring in every member of the group, justify 

 us in associating together the various individuals composing it as members of a natural 

 family, at the same time that they enable us to separate that family from those which 

 in respect of muscular arrangement most nearly approach it. These modifications are 

 most observable in the muscles of the wing, and to a less extent in those of the leg, 

 and stand in direct relation to the habits of the various members of the group. 



The wing of the Penguin is useless as an organ of flight, but is of first-rate importance 

 as a paddle wherewith the bird may propel itself through the water. In accordance 

 with this modification in function of the wing, we find an enormous development of the 

 muscles which act at the shoulder joint, that is, on the wing as a whole. These muscles, 

 together with those which act upon the scapula, are developed in the Penguin to an 

 extent observable in no other bird, and enable the wing, converted into a paddle, to 

 act as a powerful propulsive organ of the body of the bird through the relatively dense 

 medium in which the greater part of the life of the animal is passed. This arrange- 

 ment would be superfluous in the case of birds adapted to an aerial existence, the medium 

 ill which they live offering much less resistance to locomotion than the water in which 

 the Penguin spends the greater part of its life. On the other hand, the atrophy of the 

 muscles of the forearm and hand of the Penguin is consequent upon the comparative 

 fixity of the joints below the elbow, and prevents the performance of those delicate 

 movements of flexion, extension, and rotation that are essential to flight — movements, 

 the ability to perform which would be positively prejudicial to an organ whose principal 

 function is that of an oar or screw. 



The leg of the Penguin, excej)t in respect of the great development of the muscles 

 as a whole, does not present any peculiarities worthy of note beyond those already referred 

 to at page 129. 



The most striking features of the muscular system of the Spheniscidse, apart from 



(ZOOL. CHALL. EXP. PART XVIII. — 1883.) SIB 



