Head 
conveyed through the tear canals {canaliculi lacn- 
males) in the upper and lower evelids {palpebrae 
superior et inferior) to the lacrimal sac {saccus lac- 
rimalis) located at the medial canthus (angulus 
oculi medialis). The lacrimal sac represents the en- 
larged proximal portion of the nasolacrimal duct 
{ductus nasolacrimalis). Macroscopically, the ac- 
cessory lacrimal glands are grayish-white to yellow 
in color. 
Histologically, thev are compound and tubuloalveolar in structure. 
The glandular acini are lined bv a simple laver of columnar cells. The 
cells of the glandular epithelium are large, with relatively small, round 
nuclei basallv located. The cvtoplasm is verv finely granulated. 
2.24 NASOLACRIMAL DUCT 
Lacrimal secretions drain from the orbit to the 
nasal vestibule through the nasolacrimal duct {duc- 
tus nasolacrimalis). As there is no lacrimal bone in 
the European hamster, the duct exits the orbit 
through the infraorbital canal {canalis infraorbi- 
talis) of the maxillary bone, accompanied by vessels 
and nerves. Emerging from the infraorbital canal, 
the duct runs along the lateral wall of the maxilla 
covered only by muscle. It penetrates the nasal 
cavity through a small oval foramen located be- 
tween the maxilla and incisive bone, at about the 
level of the rostral end of endoturbinal I (Jensen, 
1977). It then runs along the internal surface of the 
incisive bone, ventromedial to the root of the incisor 
(Figs. 2-12, 2-13), terminating in the nasal vesti- 
bule at the level of the incisive duct. 
The terminal portion of the nasolacrimal duct is lined with multi- 
lavered unkeratinized squamous epithelium, but for most of its length, 
it is of double-iavered prismatic transitional epithelium (Jensen, 1 977). 
In certain places, this epithelium resembles ciliated epithelium. 
2.25 CRANIAL AND FACIAL 
VASCULARIZATION 
2.25.1 Arteries 
Arterial blood is carried to the head by branches 
of the common carotid {a. carotis communis) and 
the vertebral {a. vertebralis) arteries. The common 
carotid divides at the level of the thyroid gland into 
the internal {a. carotis interna) and external carotid 
{a. carotis externa) arteries. The external carotid 
first gives off the occipital artery {a. occipitalis) to 
the neck and then the lingual artery {a. lingualis) to 
the tongue. The continuation of the external carotid 
is called the maxillary artery {a. maxillaris). It 
gives off the common vascular stem from which the 
arteries to the masseter {a. massetenca) and the 
cheek pouch {a. bursa buccalis) originate. Also 
coming off this common vascular stem are the trans- 
verse facial artery {a. transversa faciei) to the zygo- 
matic arch, the auricular arteries {aa. auricularis 
caudalis et rostralis) to the ear, and the superficial 
temporalis artery {a. temporalis superficialis) to the 
temporal region, respectively. The maxillary artery 
runs to the incisura vasorum facialium and supplies 
the face as the facial artery {a. facialis). 
The internal carotid artery (Fig. 2-70) extends 
to the caudal edge of the mastoid process of the 
temporal bone {os temporale, pars mastoidea). 
Here it separates into a dorsal and a ventral branch. 
The ventral branch {a. intercarotica rostralis) enters 
the cranial cavity through the jugular foramen (for- 
amen jugular e), at the level of the hypophysis, be- 
tween the basisphenoid and the mastoid process, 
and supplies the base of the brain rostral to the 
hypophysis. The caudal portions of the brain are 
served by the basilar artery {a. basilaris) and its 
branches, the rostral and caudal cerebellar arteries 
{aa. cerebelli rostralis et caudalis). The dorsal 
branch extends dorsally along the bulla. Rostral to 
the bulla tympanica, it divides into a ventral branch 
{a. maxillaris interna) which runs through the 
pterygoid to the orbit, nose and palate, and into a 
dorsal branch which enters the cranium, runs lat- 
eral to the brain and finally becomes the internal 
ophthalmic artery {a. ophthalmica interna) which 
accompanies the optic nerve. The internal carotid 
artery does not wind through the base of the crani- 
um nor within the cranial cavity, a pattern also 
characteristic of the rabbit (Mone, et ai, 1973) and 
the rat (Wells, 1968; Horber, et al., 1974). The 
nomenclature and distribution of some important 
arteries of the brain can be seen in Figure 2-70. 
2.25.2 Venous Drainage of the Skull 
and the Ophthalmic Plexus 
The external jugular vein {v. jugulans externa), 
the principal vessel draining the head, is formed 
from the junction of the linguofacial vein {v. linguo- 
facialis) and the maxillary vein caudal to the lower 
jaw (Figs. 2-58, 2-74). At the level of the incisura 
25 
