REPORT ON THE ANATOMY OF THE PETRELS. 2o 



anterior end of the muscle on the breast close to the symphysis furculce, and goes to 

 the skin of tbe lower and anterior aspect of the neck. 



Pectoralis secundns. — This muscle is also well developed, but though broad is 

 usually short, extending for not more than one-third, one-half, or sometimes two-thirds 

 the length of the sternum. In Pelecanoldes, however, it is much longer, extending to 

 nearly the end of that bone, and in Procellaria, Garrodia, Fregetta, and Pelagodroma 

 its extent is nearly as large, in which cases it extends beyond the posterior margin of 

 the deep layer of the first pectoral. 



It arises from the antero-superior part of the carina sterni, and from the body of the 

 bone external to that, from the greater part of the coraco-furcular membrane below the 

 pectoralis tertius, from the symphysis furculce, and from a greater or less extent of 

 the antero-inferior border of the coracoid bone. Its insertion is by the usual tendon on 

 the superior aspect of the humerus, behind the much smaller tendon of the third pectoral. 



In the Albatrosses the pectoralis secundus is unusually short, and broken up into 

 four cpiite separate parts, which unite before passing the shoulder-pulley. This arrange- 

 ment is clearly shown in fig. 2 of Plate III. representing the muscle in Diomedea brachyura. 

 In the other Petrels, the muscle is much more homogeneous, and only separable by 

 dissection into its various component parts. 



Pectoralis tertius. — This muscle (PI. III. fig. 2, p. 3) is always well developed in the 

 Tubinares, in the form of a broad, thin band, more or less parallel with the coracoid, 

 occupying the superior half of the broad space between that bone and the furcula, its 

 fibres arising chiefly from the strong membrane between these bones, sometimes with 

 additions from the anterior margin of the coracoid, or from the body of the sternum 

 close to the middle line. 



Tensor patagii brevis and longus. — These muscles have always a common, rather thin 

 and flat fleshy belly, arising from the extreme upper end of the clavicle, and receiving, in 

 addition, special small slips from the surface of the great pectoral. From this fleshy 

 belly spring two tendons, of which one always forms the marginal patagial tendon, and 

 must therefore be considered as the tensor patagii longus. Both the tendons are con- 

 nected, close to their origin, by fibrous slips to the humeral crest, from which indeed 

 they might be said to arise, receiving then the main muscular belly. The connection of 

 the marginal tendon with the humerus is always provided with a small tract of strong 

 elastic tissue (vide PL IV. fig. 7, t.p.l'.), and another such tract of longer extent is found 

 on its course opposite the bend of the elbow (PI. IV. figs. 3 and 7). 



In other respects the development and distribution of these tendons differs much in 

 different groups of genera, and their arrangement will therefore be here considered 

 seriatim. 



It is in the Oceanitidse that the disposition of the tendon of the tensor patagii 

 brevis (t.p.b.) is simplest, it here, in all the four genera, passing straight downwards 



(ZOOL. CUALL. EXP. PART XI. 1882.) L i 



