REPORT ON THE SPHENISCIDyE. • 9 



strongly curved downwards behind the lachrymo-nasal fossa, while in the latter this curve 

 is much less strongly pronounced in consequence of the jugal and quadrato-jugal elements 

 being prolonged backwards almost in a straight line with the maxillo-jugal element, and 

 without the intervention of a well-defined angle such as exists in UudijjJtes. In conse- 

 quence of this arrangement, when viewed from the side, the skull of Eudijptes seems to 

 diminish in depth to the base of the upper jaw much more rapidly than does that of 

 Spheniscus. In respect of the form and curvature of the zygomatic arch the skulls of 

 Pygosceles and of Aptenodytes agree with that of Eudyptes, and differ from that of 

 Spheniscus. 



The lower jaw of every species of Penguin is composed of the same number of elements 

 as is that of other birds. In the adult they unite to form a single mass, in which, however, 

 traces remaia of the sutures which originally separate the component elements. 



In Eudyptes each ramus of the lower jaw is rhomboidal in form, the broadest part of 

 the bone, which corresponds to the shorter diagonal of the figure, being placed opposite 

 the middle in length of the ramus, whence the bone tapers to a point anteriorly and 

 posteriorly. Immediately below the middle of the upper border of the ramus is a depres- 

 sion, which in EudypAes chrysocome from the Falklands is perforated to form an open 

 foramen. In the other species of Eudyptes it is blind. From this, which may be named 

 the anterior foramen, an indication of the suture which originally separated the dentary 

 from the posterior elements of the ramus, extends with a slight obliquity downwards and 

 backwards. This suture is also clearly indicated on the inner surface of the ramus. Im- 

 mediately in front of the articular surface of the lower jaw-bone there is a second or pos- 

 terior foramen which completely perforates the ramus in every species of Eudyptes. It is 

 small in size, and of an oval form. 



The articular surface of the lower jaw-bone is irregular in form and adapted to the 

 lower end of the quadrate bone. It is bounded internally and posteriorly by a well- 

 developed " angular " process. Of these the internal is shorter and broader than the pos- 

 terior. A coronoid process does not exist. The lower surface of the internal process is 

 deeply grooved by the pterygoid muscle, and is separated from a second groove on the 

 outer side of the bone by a ridge which forms part of the lower border of the jaw. The 

 latter groove affords insertion to the digastric muscle. 



The lower borders of the rami of opposite sides in every species of Eudyptes closely 

 approach one another in the middle line inferiorly. This is due to the gradual widening 

 of the bones in front of their articular extremities, and serves at once to distinguish the 

 skull of any species of EudyjJtes from that of any other genus. In the skuUs of other 

 genera the inferior inter-ramal space narrows gradually from the articular to the free 

 extremity of the lower jaw-bone, whereas in Eudyptes that space is suddenly contracted 

 opposite the middle in length of the ramus. 



In Spheniscus the rami of the lower jaw are relatively longer and more slender than 

 in Eudyptes, and do not present the rhomboidal form which is characteristic of those 



(ZOOL. CHALL. EXP. — PART XVIII. — 1883.) S 2 



