148 Dli. J. MTJUIE ON THE WHITE-BEAKED BOTTLENOSE. 



presence of a number of blood-vessela and nerves. These are 

 situate between this and the upper muscle, towards tlieir pos- 

 terior aspects, and have a direction downwards and forwards. I 

 presume them to be terminal branches of the temporal or supra- 

 orbital roots. 



The third layer, as my drawing shows, is likewise fan-shaped, 

 but less broad than the two preceding, and consequently di- 

 minished in maxillary attachment. Its upper tendinous iusertiou 

 beneath the last is upon the lower surface of the sac ; and fibres 

 proceed to the deeper chink of the blow-hole, a small fasciculus 

 going to the front of the orifice. The latter fibres appear there- 

 fore, by a pulley kind of action, to draw the centre of tlie blow- 

 hole forwards ; the others tract outwards and backwards ; so that 

 their combined force is a dilator of the upper narial orifice. 



The anterior portion of the fourth, fan-shaped layer, compared 

 Avith the others, is immensely strong. Its outer, semicircular 

 border is fixed upon the upper surface of the maxillary bone, its 

 malar portion to the anterior end. Tiie muscle's posterior border, 

 partially covered by that next to be described, is concave and looks 

 upwards ; its anterior border has a more sinuous sweep, and 

 reaches over the premaxillary sac and the overlying blubber, join- 

 ing as a bridged band its fellow of the opposite side. An apo- 

 neurosis also connects the upper hind border of the muscle with 

 the naso-frontal sac. 



As regards the use of the muscle, the front arch, in continuation 

 with its opposite moiety, is a powerful compressor of the nasal 

 blubber, and consequently a contractor of the premaxillary sac. 

 Under certain conditions, also, the said transverse band may close 

 the blow-hole. But, again, if the transverse fibres, which de- 

 cussate slightly with those of the two superficial layers, act in 

 conjunction with the latter, which seems not improbable, they 

 then would have a tendency to open the blow-hole. 



A lougish, narrow, triangular muscle of moderate thickness 

 lies posterior to the last, and, as said, partly overlapping it. The 

 upward tendinous apex partially covers the naso-frontal sac, and, 

 behind the mouth of the maxillary sac, winds narrowly rouiul the 

 bone, and is inserted in front of the nasals. Its main oilico seems 

 to be to compress the posterior or nasolronlal sac. 



The fifth layer more fully discloses the lateral and posterior 

 sacs, iuasmucli as the muscle or muscles lie outside or in frout 

 of these. The fieshy parts exposed may either be cousidered a 



