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60 AXATOMY.
the tympanic branch of the glosso-pharvngeal (Jacobson's) nerve. Ou
the border between the posterior and the inferior surfaces, internal to
the jugular fossa, is the aqueductus cochlea, which transmits a vein from
the cochlea to join the internal jugular vein. In the internal portion
of the jugular fossa is a foramen for the auricular branch of the pneumo-
gastric nerve (Arnold's nerve).
The Tt/mpanic Portion forms part of the roof of the external audi-
tory meatus, and is that ]>art of the glenoid fossa which lies beloAV
and posterior to the glenoid fissure. It is irregular in outline, and is
wholly made up of compact tissue. When examined externally, it pre-
sents a U-shaped portion which bounds three-fourths of the external
auditory meatus ; which opening leads direct to the tympanic mem-
brane. The remaining or up])er boundary of the meatus is formed by
the squamous portion of the l)one. The curve of the U is roughened
for the attachment of the cartilage of the ear. The tympanic division
extends inward and downward, encasing the base of the styloid process.
This division terminates anteriorly in the vaginal process and poste-
riorly in the glenoid fossa. It is concave in form, and receives the
upper portion of the jiarotid gland. It terminates in the point opposite
the spinous process of the sphenoid bone, at the commencement of the
opening for the cartilaginous portion of the Eustachian tube.
The Styloid Portion is of hard consistency, long and tapering, point-
ing downiward, inward, and forward in the direction of the great cor-
nu of the hyoid bone ; its average length is about one inch, though
sometimes it is greater, com])I;cating surgical operations in the region
through which it passes. It is situattd directly in front of the digastric
fossa and behind the vaginal ])roccss, which in great part surrounds it.
It gives origin to the stylo-jiharyngeus, the stylo-glossus, and the stylo-
hyoideus muscles ; also to it the etylo-hyoid and the stylo-maxillary
ligaments are attached. The mastoid portion is the enlarged roughened
portion situated at the posterior inferior extremity of the bone. It
assists in forming the masto-occi])ital and the masto-parietal sutures,
the mastoid ridge separating it from the squamous })t>rtion of the bone.
It is divided into two ])ortions, tlie mastoid and the posterior mastoid,
by tlie extension over it of the superior semicircular line from the occip-
ital bone, which line continues its curve, terminating at the extremity
of the mastoid process. The last is large, extending downward and
forward behind the external auditory meatus and the tympanic jxirtion
of the glenoid fossa. It is small (hiring infancy, l)ut increases and
becomes of large size in the adult, especially in individuals with large
and powerful muscles. It serves for the attachment of the sterno-cleido-
mastoideus, tlie splenius cajiitis, and the trachelo-mastoid nnisdes, the
two former extending tlieir attachment along tlie su]>erior semicircular
line f»f the occipital bone. The internal ])ortion of the mastoid process
is full of cells, which comnuuiicate with the middle car. On the inner
portion and at the base of the process is a deep groove, the digastric
fossa, for the attachment of the digastric nuiscle ; and on the inner side
of the groove and parallel with it is the occipital groove for the occipital
artery.
Between the mastoid and the styloid processes, and immediately in