66 THE VOYAGE OF H.M.S. CHALLENGER. 



inserted into the base of the last caudal vertebra, or ploughshare bone, as well as into 

 the spinous processes of the three preceding vertebrse. 



The second or posterior portion of the muscle (transversaire-^pineux of Gervais and 

 Alix) consists of shorter fibres, which arise from the upper surfaces of the transverse 

 processes of all the caudal vertebras. They pass obliquely backwards and upwards, and are 

 inserted into the bifid spines of the last four caudal vertebrae, including the plough- 

 share bone. A few of the fibres of this portion of the muscle are, moreover, inserted into 

 the fibrous capsule of the uropygium. 



The two portions of the levator coccygis are quite continuous with one another, 

 and form, as it seems to me, a single muscle, the distinction between its parts lying 

 rather in the difi"erence in length of the fibres which compose them than in any clearly 

 defined separation of these parts from one another. 



Action. — Through the action of the muscle of one side, the tail is abducted. When 

 both muscles contract simultaneously, the tail is elevated. 



Relations. — The anterior portion of the muscle hes in contact with the origin of the 

 biceps cruris on its outer side. The posterior portion is to a large extent concealed by 

 the caudal gland which rests upon it. 



Nerve supply. — The dorsal branches of the coccygeal nerves give ofi" several twigs 

 to this muscle. 



Variations. — In Eudyptes chrysocome from Kerguclen, as well as in a specimen from 

 the Falklands, I observed that the slip of this muscle which is inserted into the capsule 

 of the caudal gland is of relatively larger size than in other species. 



In Eudyptes chrysolophus this slip is given ofi" from the middle in length of the 

 second portion of the muscle. In several species, e.g., Sp>heniscus 'magellanicus and 

 Eudyptes chrysocome from Kerguelen, the transverso-spinal portion is provided with a 

 series of tendons of insertion, one of which is attached to the spinous process of each 

 of the caudal vertebrae. That to the ploughshare bone is stronger than the others, and 

 appears to be formed by the junction of several distinct tendons corresponding to the 

 separate vertebrae which unite to form the ploughshare bone. It would therefore appear 

 that the levator coccygis is composed of a series of distinct transverso-spinal slips, each 

 of which passes between the transverse process of one vertebra and the spine of that 

 succeeding, and that in some birds these remain distinct throughout life, while in others 

 their tendons become more or less fused together, and give rise to the arrangement above 

 described in Eudyptes chrysocome from Tristan d'Acunha, in which separate tendons to 

 each of the caudal vertebra are no longer recognisable. 



2. Tnterspinales. 

 In addition to the levator caudas above described, there are a number of fleshy slips 



