SKELETON OF QUADRUMANA. 



531 



Uowlei (My cUtswbinus) LXix 



lu the Red Howler (yMycetes seniculus, fig. 350) the superocci- 

 pital region is ahnost flat and vertical, at right angles with the 

 parietal surface, from which it is separated by a well-defined 

 ridge : the foramen magnum looks almost directly backward. 

 The maxillo-premaxillary sutures demonstrate the junction of the 

 premaxillaries with the nasals. The ectopterygoids much exceed 

 the entopterygoid plates in size. The 

 large malar foramen communicates with 

 the orbit : the suborbital foramina of 

 the maxillary are two in number, and 

 small. The chief feature of peculiarity 

 in the skull of the Howler is the extra- 

 ordinary depth of the mandibular rami, 

 especially of their angular and ascend- 

 ing portions. This development relates 

 to the protection and support of the 

 still more extraordinarily developed 

 hyoidean and laryngeal apparatus — the 

 organs of the loud and dissonant cries which have procured for 

 these South American Monkeys their common name. The 

 superior length of the postglenoid process, in relation to the 

 larger and heavier lower jaw, is worthy of notice. An obtuse 

 paroccipital ridge extends from the condyle to the mastoid ridge. 

 The precondyloid, jugular, and carotid foramina all open into 

 an irregular fossa between the petrosal and paroccipital ridge. 

 There is a small venous foramen outside the mastoid, and a 

 second at the anterior border of the squamosal. The hyoid arch 

 is reduced to the basi- and thyro-hyals ; but the former is 

 enormously developed, and expanded into a capacious sac mth 

 thin walls, and a posterior opening, admitting a laryngeal pouch. 

 A narrow transverse plate descends from the roof of the bony 

 sac. The cerato-hyals are obsolete. The thyro-hyals long, for 

 suspending the sac to the upper angles of the large thyroid car- 

 tilage. 



There is much greater diversity, and more marked ascending- 

 steps of structure, in the skull of the ' Old World ' than of the 

 ' New World' Monkeys. No Catarrhine shows ossification of 

 the tentorium ; and in all the preclinoid, as well as postclinoid, 

 processes defend the sella. The same remark, as to concur- 

 rence of immature proportions of cranium and jaws with in- 

 fantile stature, applies to the Catarrhine as to the Platyrrhine 

 Quadrumana. But the larger s^^ecies of the lower groups ( Cj/- 

 nocejyhalus, Papio, e.g.) show more carnivorous or brutish pro- 



M M 2 



