lo4 MK. W. K. PAEKER ON THE STEUCTUBE AND 



Not less unmistakeable is the mammalian nature of the small, late, long distinct basi- 

 temporals (Plate XIV. fig. 2, h.t.) or " lingul-de ;" in Struthio camelus (B.), a stage of the 

 embryo three weeks earlier at least, these bones had not only coalesced with each other, 

 but also with the basisphenoid. In young ripe Crocodiles, the same stage as this Cas- 

 sowary, a mere trace of the distinctness of these bones is seen. In Chelone mydas, at 

 the same age, the sutm-es can be traced, and often for a long while in that group the 

 basitemporals do not coalesce as I have seen in Emys Europoea, and as is well shown in 

 Dr. Gray's figm-e of Cyclanosteus senegalensis (Zool. Proc. 1864, pt. 1. p. 96) ; but in 

 that order, as in most Reptiles, these bones meet at the mid line, and extend through 

 the entire substance of the basis cranii. But in the Mammalia, where for the most part 

 these bones are quite lateral and very small, they continue distinct in some cases, e. g., 

 in the Walrus {Trichechus), until the creature is well nigh full grown. Still in the 

 Cassowary they retain the ornithic and reptilian function of forming a floor to, and 

 helping to enring the internal carotid artery {i.e.), a vessel which takes shelter in the 

 prootic, or the tympanic, or in both, in the Mammalia. The anterior and posterior 

 pterygoid processes {a.p.,p.r.p.) are perfectly struthious, and there is not much to remark 

 upon in them, save that they come very close to the same parts in the Emu, as in that 

 bird the Eustachian tubes are merely overshadowed by bone, and open into one common 

 palatine slit between and behind the (struthiously distinct) middle nares. 



The " rostrum" of the basisphenoid (r.b.s.) is somewhat stronger than in the Emu, 

 and is intermediate between that of the latter bird and the Rhea ; it passes under the 

 septum for a shorter distance than is usual in the Struthionidae. The broad part of the 

 basisphenoid is such as would be seen in the young Fowl if four-fifths of the basitemporals 

 were cut away, leaving only a remnant at each hinder angle ; thus exposing the sjTichon- 

 drosis of the two mesial bones, and laying bare the Eustachian trumpets. A layer of 

 fibrous tissue separates the "rostrum" from the coalesced trabeculae (Plate XIV. fig. 8) 

 up to the high prepituitary part of the basisphenoid. The alisphenoids (Plate XIV. 

 figs. 1, 5, & 6, a.s.) are relatively higher than in the other Ostriches, and they are not 

 so ornithically transverse ; there is a great approach to the lateralness seen in the Croco- 

 dile and the Mammal. They are ossified, save at the postfrontal spur {p.f.), in front 

 of the divided "foramen ovale," and below; but the upper basisphenoidal lamella has 

 nearly reached them on each side (Plate XIV. figs. 5 & 6) ; the " foramen rotundum " 

 (5, a) is principally bounded by the cartilage which underlies the alisphenoid anteriorly. 

 A broad right-angled space lies between the upper arched margin of the prootic and the 

 sinuous posterior margin of the alisphenoid (Plate XIV. figs. 5 & 6) ; in the Fish this 

 space is filled up by the great "pterotic" cartilage-bone, which has in front of it, and 

 interlocked into it, an almost equally developed external alisphenoidal epiphysis — the 

 postfrontal. The alisphenoid, in this as in the other " Struthionidae," is a convexo- 

 concave thick bone, its scooped part being within ; it has no central " fontanelle " as in 

 many birds ; but, as is the rule in the whole class, an oblong fontanelle intervenes 

 between it and the margin of the orbito-sphenoid (Plate XIV. fig. 1, o.s.). 



