Elementary Text-Book of Zoology: V.2

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1885 edition. Excerpt: ... mandibular arch is firmly connected with the skull. The mandibular suspensorium and the palato-quadrate are in direct connection with the cartilaginous cranium, and form on either side a wide outstanding infra-orbital arch, the anterior end of which either remains free or fuses with the ethmoid cartilage. The ossification appearing at the end of the suspensorium gives rise to the quadrate, while a membrane bone, almost hammer-shaped and overlying the suspensorial cartilage, is called the squamosal or perhaps more correctly tympanic (Ty). Two membrane bones extend forward along the lower side of the palato-quadrate bar--the pterygoid (Pt) behind and the palatine (PI) in front. The palatine is transversely placed behind the vomer. The outer arch of the upper jaw, formed by the prcemaxillary and maxillary bones (Jmx, Mx) may by means of a third posterior bone--the quadrato-jugal (J)--be continued back to the quadrate, but in many Perennibranchiata it is incomplete, the maxillaries being absent. The skeleton of the visceral arches is more or less considerably reduced in correspondence with the retrogression of branchial respiration. In the perennibranchiate Amphibia (Amphibia with gills throughout life) the visceral arches are more numerous, and present an arrangement similar to that found only transitorily in the larvae of the other forms. In the Salamandrina, in addition to the hyoid arch, the remains of two branchial arches persist; while in adult Batrachians only a single pair of arches is retained on the hyoid bone. This branchial rudiment is attached to the posterior edge of the body of the hyoid bone, and serves as a suspensorium for the larynx. In the pectoral girdle three parts may be distinguished--the scapula, the prcecoracoid, and the...