TARSIUS SPECTRUM 119 



a fact which permits of the conclusion that the extremities, and particularly 

 the upper extremities, are capable of the simplest motor patterns only 

 This index of motor organization is an added argument supporting the view 

 that tarsius is but nieagerly endowed in behavioral reactions. 



Adjacent to the ventromedian sulcus of the fourth ventricle, and beneath 

 the ventricular floor, is the dense circular bundle representing the second 

 portion of the seventh nerve (Ny). Lateral to this facial bundle are the 

 heavy fibers of the abduccns nerve (N6), which make then- way directly 

 forward toward the trapezoid body (Ctr). They arise in the abducens 

 nucleus which is situated ventral to the triangular nucleus. It is of interest 

 in this connection to note the diffuse character of the triangular nucleus. 

 Its boundaries have none of the definition characteristic of the higher species. 

 Many fibers traverse it, giving the impression of a nuclear territory which 

 has not yet thoroughly established its own autonomy. 



The origin of the Deiterso-spinal fibers (DT) is clearly seen. The 

 restiform body (ICP), the substantia gelatinosa of Rolando (NR) and 

 the descending trigeminal tract (Trd) all occupy their usual positions. 

 The trapezoid body (Ctr), with its large superior olive (So) and its extensive 

 decussation, indicates the degree of development in auditory conduction. 

 The reticular formation(Ref) is extensive and contains no discretely ditler- 

 entiated territories. 



Adjacent to the raphe, the posterior longitudinal and predorsal bundles 

 (PL, PD) appear in the unusually large dimensions characteristic of tar- 

 sius. The mesial fillet (Mf) is still partially obscured by the crossing fibers 

 of the trapezoid decussation (Ctr), while the relatively small size of the 

 pyramid (Py) is decisively shown in comparison to the rest of the section. 

 It is noteworthy that the entire trapezoid body remains without being 

 submerged by pontile fibers. Tarsius is the only one of the primates in 

 which this is the case. Although the corpus trapezoideum is only partially 



