REPORT ON THE ANATOMY OF THE PETRELS. 40 



The scapula is a slender, slightly curved bone, presenting no special peculiarities. Its- 

 acromial process is prolonged inwards and forwards to nearly, or quite, meet the posterior 

 end of the clavicle. The angle it forms with the coracoid varies very nuu-h in different 

 genera, being most acute in Pelecanoides, whilst in the Oceanitidse it is hardly, if at 

 all, less than a right angle (vide PI. VII. fig. 8, Fregetta). Procellaria and Cymochorea 

 resemble the other Procellariidse, the coraco-scapular angle being in them obviously 

 (t.c, fig. 6) acute. 



The clavicles are always well-developed, strongly convex forwards as seen from the 

 side, and forming a more or less widely-open U when seen from in front. Their posterior 

 ends are produced backwards to unite, by ligament, with the acromial process of the 

 scapula. The symphysis is usually somewhat dilated and thickened and closely apposed 

 to the anteroinferior angle of the sternum, to which it is connected by ligament. 

 In Pelecano'iih's the clavicular arch is more V-shaped, its limbs diverging but little, and 

 the symphysis develops a firm articulation with the carina stem! (vide PI. VII. figs. 

 3, 4) as in Phalacrocorax, Sula, Plotus, and Phaethon of the Steganopodes. In 

 the Oceanitidse (vide PI. VII. fig. 8) the symj)hysis furcidce has a strong, curved 

 hypocleidial process, directed downwards and backwards, very much more developed 

 than the corresponding part in any Procellarian genus, even Cymochorea or Procellaria 

 (t.c., fig. 6). 



Anterior Extremity. — The humerus (PI. VI. figs. 9-11, where that of Majaqueus 

 cequinoctialis is figured) is long, with a cylindrical shaft, often much conqjressed 

 distally in such a way that the outer margin of the bone with its condyle is 

 anterior and the inner one with its condyle posterior. The head is but little elevated 

 above the general level of the proximal end of the bone. The pectoral ridge is promi- 

 nent and triangular, but short, and the deltoid impression extends only as low as 

 its distal termination. Behind the deltoid impression is a linear one for the latissvm us 

 dorsi. The bicipital surface is well developed, the lesser trochanter strong and re- 

 curved ; it is excavated behind and below by a deep infra- capitular fossa, bounded 

 above by the strong interfossal ridge, the supra-capitular fossa being a more shallow 

 concavity. The tubercle for the insertion of the q)€Ctoralis secundus is strong, and is 

 situated at the commencement of the pectoral crest, just anterior to the articular 

 head. Below and anterior to it is an oval depression, often large, for the pectoralis 

 tertius. The external condyle is prolonged obliquely upwards and inwards on the 

 anterior surface of the bone ; the capitellum is distinct, and separated by a slight notch 

 from the internal condyle. The olecranar fossa is shallow and prolonged upwards into 

 a smooth, slightly excavated triangular area. The impression for the brachialis anticus 

 is deep and oval. 



Above the external condyle there is a very strong, forwardly-directed epicon- 

 dylar process, from which arises the more superficial of the bellies of the extensor 



(ZOOL. CHALL EXI\ PART XI. — 1882.) L 7 



