422 ANATOMY OF VERTEBRATES. 



a moderately long and slender piece, bent upon itself at an acute 

 angle. The upper portion, wedged between the maxillary and 

 frontal, is the thickest : the lower and more slender branch is 

 bent downward and backward, circumscribing the orbit anteriorly 

 and below, and continued by ligament or fibro-cartilage to the 

 short obtuse zygomatic process of the temporal. There are no 

 lacrymal bones. The anterior two-thirds of the middle and under 

 surface of the maxillary is traversed by a vascular and dental 

 groove : rudiments of teeth hidden and buried in the gum are 

 usually found in this groove. The squamosal is a comparatively 

 small, but strong and thick triangular bone : the upper angle 

 represents the expanded squamous part in land Mammals, and is 

 articulated by broad dentated sutural margins to the frontal and 

 exoccipital : its anterior border is grooved for the reception of the 

 alisphenoid : the lower angle is, as it were, truncated, and presents 

 a rough surface for the attachment of the petrotympanic : a short 

 obtuse anterior angle bends forward as the zygomatic process : 

 the under surface presents a smooth shallow cavity for the 

 condyle of the lower jaw ; the inner border of the glenoid surface 

 being produced downward into a slender styliform process. The 

 tympanic, here, as in other Cetacea, presents a peculiar conchoidal 

 shape, and is extremely dense in texture. An outer plate bends 

 over the thicker, seemingly involuted part, like the outer lip of the 

 univalve Pyrula, The ^ Eustachian ' outlet is at the fore part; and, 

 besides this, may be noted, in Physeter, the ^ involute convexity,' 

 with its ' outer ' and * inner ' lobe, the ' overarching plate,' and 

 the ' rough tympanic process,' by which it joins and coalesces 

 with the 'petrosal:' this is characterised by a deep fossa. ^ The 

 condyle of the mandible projects from the posterior part of the 

 base or ascending ramus, which is compressed and produced into 

 a low obtuse coronoid process above, and into a similar angle 

 below: a Avide excavation, beginning on the inner side of the 

 ascending ramus, deepens and contracts into the dental canal, 

 which enters the substance of the horizontal ramus : a fissure is 

 continued along the inner side of the ramus from this canal, and 

 is the sole indication of a compound structure of the jaw. The 

 vessels and nerves emerge from several foramina at the outer side 

 of the ramus, where it is attached by its long symphysis to its 

 fellow : the ui)per border of the symphysial part of the ramus is 

 excavated by a continuous dental canal or groove, now somewhat 

 resembling that in tlie upper jaAv. The length of the symphysis 

 in the fatal Cachalot is three-fourths that of the rest of the 



* XV11I-. p. 526, figs. 220, 225. 



