1844.] Linnean Society. 213 



dification, the description of the muscles of the tails of birds given 

 by Cuvier ; the latter he describes in the following terms : — 



" Upon the sacro-coccygeal muscle, which is exceedingly large and 

 powerful in this bird, there is placed a mass of cellular substance some- 

 what of a triangular shape, measuring about five inches at the base, 

 and each lateral line extending from the base to the apex about six 

 inches ; the base is situated towards the tail, and extends in this di- 

 rection almost as far as the last caudal vertebra ; thus there is not 

 the space of an inch between the quills of the upper tail-covert and 

 those of the true tail, while the apex of the triangular mass extends 

 nearly to the lumbar extremity of the sacrum ; it is wider than the 

 muscle upon which it lies, and extends over it at each side full half 

 an inch. This triangular mass is much thicker below than above : 

 here it is full three-quarters of an inch thick, whilst at the apex it is 

 not half this thickness. It is covered on its sacral surface by a 

 thin fascia, and is connected to the muscle beneath it by loose cel- 

 lular texture, which can be easily broken down by the handle of a 

 scalpel ; but it has a membranous and closer connection, and towards 

 its base it is more intimately attached by muscular fibres proceeding 

 from the elevator muscles beneath, which are lost in the fascia cover- 

 ing its sacral surface. 



" The quills of the upper tail-covert are inserted obliquely into this 

 triangular mass of cellular substance, each quill having its peculiar 

 capsule, which seems to be formed of condensed cellular membrane : 

 between each quill there are small muscles, the fibres of which run 

 in parallel lines extending from one quill to the other ; and besides 

 these muscles there are other small ones, the fibres of which run ob- 

 liquely in such a direction as somewhat to resemble the letter V; the 

 interstices of these muscles are filled with cellular substance, 



" By the powerful action of the sacro-coccygeal and the sacro-su- 

 pracaudal muscles, the true tail is elevated, and at the same time the 

 upper tail-covert is raised perpendicularly and supported by the pro- 

 per tail, and perhaps the swelling of these muscles in their contrac- 

 tion exerts some influence in spreading the feathers of the upper tail- 

 covert. The principal agents in this office are the small muscles 

 situated between each quill, by the contraction of which the quiUs 

 are brought closer together, and consequently the opposite ends of 

 the feathers are proportionately separated from each other. The 

 small muscles of which the fibres diverge have not only the power of 

 contributing, by their contraction, to the spreading of the feathers 

 of the upper tail-covert, but they exert considerable influence in 

 raising the feathers perpendicularly. There can be no doubt also. 



No. XXII. — Proceedings of the Linnean Society. 



