File:Chordate morphology (1962) (20422970480).jpg

Title: Chordate morphology
Identifier: chordatemorpholo00joll (find matches)
Year: 1962 (1960s)
Authors: Jollie, Malcolm
Subjects: Morphology (Animals); Chordata
Publisher: New York, Reinhold
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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alisphenoid bulla eustachian tube and foramen ovole tympanic anterior lacerate fenestra groove for palatine branch of VII orbitosphenoid porasphenoid exoccipital process occipital condyle .foramen magnum
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Figure 3-6. Details of base of the skull of a (ventral aspect up). bone. The occipital bones differ in that the exoccipitals meet broadly above the foramen magnum. A postparietal is usually lacking in marsupials; in the opossum, however, it is present and is fused with the supraoccipital. The cranial capsule is relatively smaller, less rounded, and is roofed by the frontals and parietals, which meet along the midline as a sharp sagittal crest. The nasals are narrow anteriorly and much expanded posteriorly. Internally (Figure 3-5 C,D) the cranial cavity is relatively smaller, lacking a tentorium and lacking a plate-like dor- sum sellae. The clinoid processes connect from front to back on either side of the sellar depression. There is a large perpendicular plate of the ethmoid fitting into the notch of the vomers. As in the placentals, the turbinals are ossified, and, the internal foramina of the petrosal are the same. There are no frontal or maxillary sinuses. The mandible is not unusual, except that the angular process is medially rather than posteriorly directed. The hyoid (Figure 3-11 A) is much like that of the rabbit. There is a pair of small plate-like hypohyals, each tapering later- ally to a point at the attachment of the stylohyoid ligament. The hypohyals articulate with a thick body, or copula, which in turn articulates posterolaterally with a large cerato- branchial 1. y hypoglossal foramina Ijj ^jugular foramen exoccipital process fenestra cochleae foramen primitivum VII half-grown opossum as seen in a ventrolateral view The head skeleton of the opossum differs markedly from those placentals we have examined, but when compared with others, especially the insectivores, it is found to represent only an extreme. The marsupial head skeleton is best character- ized as having an unequal number of incisors above as com- pared with below, as having the jugal contributing to the articular area of the mandible, and as having a basically alisphenoid bulla (a posterior chamber from the petrosal may be added). The fenestrated palate, a confluent optic- orbital fissure, and the lack of a postparietal (the opossum is exceptional in having this bone) are typical but not ab- solutely distinctive. The appearance of a parasphenoid rudi- ment in the young is matched in several placentals (camel, flying lemur). Head skeleton of the monofreme The monotreme head skeleton can rarely be studied from actual specimens but is worth describing and illustrating. Of the three living genera found in Australia and New- Guinea, two can be compared as representatives of the group: the Duck-billed Platypus, Ormthorhynchus, and the Spiny Anteater (or Echidna), Jachyglossus. The exact details of the 44 • OSTEOLOGY AND THE MAMMALIAN HEAD SKELETON

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