DISSECTION OF THE DOG 165 



artery (a. stylo-mastoidea) — enters the stylomastoid foramen of the temporal 

 bone ; (3) an anterior auricular branch supplies the front of the ear and 

 anastomoses with the anterior auricular artery. 



A. maxillaris interna. — From the circumstance that it passes through 

 the alar canal of the sphenoid bone, the internal maxillary artery may be 

 divided into two parts, namely, (1) a part before the canal is entered, and 

 (2) a part after the canal has been traversed. The first portion of the 

 artery is now exposed, and will be observed to take a curved course towards 

 the median plane of the head, and in an oral direction, ventral to the mandibular 

 articulation. 



From the first part of the internal maxillary artery three important vessels 

 arise : (1) The inferior alveolar artery (a. alveolaris inferior) crosses the external 

 pterygoid muscle and enters the mandibular foramen. Within the bone this 

 artery contributes twigs to the teeth, and the mental artery (a. mentalis), which 

 leaves the bone by the mental foramen and assists in the supply of blood to 

 the lower lip ; (2) the posterior deep temporal artery (a. temporalis profunda 

 posterior) leaves the internal maxillary about the same place as does the inferior 

 alveolar, and curves round the oral side of the mandibular joint to reach the 

 temporal fossa, where it is expended in the muscles therein contained. One 

 of its branches accompanies the masseteric nerve through the mandibular 

 notch ; (3) just before the internal maxillary enters the alar canal it gives 

 origin to the middle meningeal artery (a. meningea media), which at once enters 

 the cranium by the oval foramen. 



N. temporalis profunda. — The deep temporal nerve, a branch of the 

 mandibular, accompanies the deep temporal artery into the temporal muscle. 



Dissection. — Remove the remains of the digastric and pterygoid muscles. 

 Sever the stylo-glossal muscle a short distance from its origin, and turn 

 it down as far as possible. Cut through the stylo-hyal bone about its 

 middle, and disarticulate its distal portion. Then carefully clean the 

 structures lying in the neighbourhood of the base of the skull and the 

 pharynx. The structures to be examined are a number of small muscles, 

 the commencement of the extra-cranial course of the last four cerebral 

 nerves, the ventral branch of the first spinal nerve, a part of the 

 sympathetic nervous system, the occipital and internal carotid arteries, 

 and the commencement of the internal jugular vein. 



M. tensor veli palatini. — The tensor muscle of the palatine velum, that 

 is of the soft palate, lies medial to the pterygoid muscles. Arising from the 

 muscular process of the temporal bone, the muscle becomes tendinous on the 

 lateral face of the pterygoid and bends round the free border of this bone to 

 end in the soft palate. 



M. levator veli palatini. — The levator of the palatine velum arises in 



m 3 



