tal sutures, seem yet to think that a derivation of noxious humours from the encephalon is more easily procured at this part than any other of the skull; and that medicines have a greater effect here, than elsewhere, in the internal disorders of the head.
Ossa Temporum, so named, say authors, from the hair's first becoming grey on the temples, and thus discovering peoples ages, are each of them equal and smooth above, with a very thin semicircular edge; which, from the manner of its connection with the neighbouring bones, is distinguished by the name of ossa squamosum.—Behind this, the upper part of the temporal bone is thicker, and more unequal, and is sometimes described as a distinct part, under the name of pars mammillaris. Towards the base of the skull, the temporal bone appears very irregular and unequal; and this part, instead of being broad, and placed perpendicularly, as the others are, is contracted into an oblong very hard substance, extended horizontally forwards and inwards, which in its progress becomes smaller, and is commonly called os petrosum.
Three external processes of each temporal bone are generally described.—The first, placed at the lower and hind-part of the bone, from its resemblance to a nipple is called mastoides, or mammillaris. It is not solid, but within is composed of cancelli, or small cells, which have a communication with the large cavity of the ear, the drum; and therefore sounds, being multiplied in this vaulted labyrinth, are increased, before they are applied to the immediate organ of hearing. Into the mastoid process, the stenomastoideus muscle is inserted; and to its back-part, where the surface is rough, the trachelo-mastoideus, and part of the splenius are fixed.—About an inch farther forward, the second process begins to rise out from the bone; and having its origin continued obliquely downwards and forwards for some way, it becomes smaller, and is stretched forwards to join with the os malæ; they together forming the bony jugam, under which the temporal muscle passes. Hence this process has been named zygomatic. Its upper edge has the strong aponeurosis of the temporal muscle fixed into it; and its lower part gives rise to a share of the masseter.—The fore-part of the base of this process is an oblong tubercle, which in a recent subject is covered with a smooth polished cartilage, continued from that which lines the cavity immediately behind this tubercle.From the under craggy part of the os temporum, the third process stands out obliquely forwards. The shape of it is generally said to resemble the ancient stylus scriptorius; and therefore it is called the styloid process. Several muscles have their origin from this process, and borrow one half of their name from it; as stylo-glossus, stylo-hyoideus, stylo-pharyngeus: to it a ligament of the os hyoides is sometimes fixed; and another is extended from it to the inside of the angle of the lower jaw. This process is often, even in adults, not entirely ossified, but is ligamentous at its root, and sometimes is composed of two or three distinct pieces.Round the root of it, especially at the fore-part, there is a remarkable rising of the os petrosum, which some have esteemed a process; and, from the appearance it makes with the styliform, have named it vaginalis.Others again have, under the name of auditory process, reckoned among the external processes that semicircular ridge, which, running between the root of the mastoid and zygomatic processes, forms the under part of the external meatus auditorius.
The sinuosities or depressions on the external surface of each os temporum are these:A long fossa at the inner and back part of the root of the mammary process, where the posterior head of the digastric muscle has its origin.—Immediately before the root of the zygomatic process, a considerable hollow is left, for lodging the crotaphite muscle.Between the zygomatic, auditory, and vaginal processes, a large cavity is formed; through the middle of which, from top to bottom, a fissure is observable, into which part of the ligament that secures the articulation of the lower jaw with this bone is fixed. The fore-part of the cavity being lined with the same cartilage which covers the tubercle before it, receives the condyle of the jaw; and in the back-part a small share of the parotid gland, and a cellular fatty substance, are lodged.—At the inside of the root of the styloid apophyse, there is a thimble-like cavity, where the beginning of the internal jugular vein, or end of the lateral sinus, is lodged.—Round the external meatus auditorius, several sinuosities are formed for receiving the cartilages and ligaments of the ear, and for their firm adhesion.
The holes that commonly appear on the outside of each of these bones, and are proper to each of them, are five.—The first, situated between the zygomatic and mastoid processes, is the orifice of a large funnel-like canal, which leads to the organ of hearing; therefore is called meatus auditorius externus.The second gives passage to the portia dura of the seventh pair of nerves; and, from its situation between the mastoid and styloid processes, is called foramen stylo mastoideum.—Some way before, and to the inside of the styloid process, is the third hole; the canal from which runs first upwards, then forwards, and receives into it the internal carotid artery, and the beginning of the intercostal nerve; where this canal is about to make the turn forwards, one, or sometimes two very small holes go off towards the cavity of the ear called tympanum: through these Valsalva affirms the proper artery or arteries of that cavity are sent.—On the anterior edge of this bone, near the former, a fourth hole is observable, being the orifice of a canal which runs outwards and backwards, in a horizontal direction, till it terminates in the tympanum. This, in the recent subject, is continued forward and inward, from the parts which were mentioned just now as its orifice in the skeleton, to the side of the nostrils: being partly cartilaginous, and partly ligamentous. The whole canal is named, Iter a palato ad aurem, or Eustachian tube.—On the external side of the bony part of this canal, and a-top of the chink in the cavity that receives the condyle of the lower jaw, is the course of the little nerve said commonly to be reflected from the lingual branch of the fifth pair, till it enters the tympanum, to run across this cavity, and to have the name of chorda tympani.The fifth hole is very uncertain, appearing sometimes behind the mastoid process; sometimes it is common to the temporal and occipital bones; and in several sculls there
