ANATOMY. 



217 





os basilare, and we cannot omit this opportunity 

 of directing the attention of all who feel anxious 

 to become acquainted with animal mechanism, to 

 study carefully the structure, connections, and uses 

 of this bone, to which there are not fewer than ten 

 pairs of muscles attached. 



The Os Sphenoidum, or sphenoid bone, (No. 3. fig 

 1.) It is situated in the middle of the basis of the 

 cranium, extending underneath from one temple 

 across to the other ; its figure is very irregular, anc 

 has been compared to a bat with its wings extended 

 This bone, at birth, consists of five portions, 

 ioined together by strong cartilages. Its connec- 

 tions are very varied and extensive, being connected 

 with all the bones of the head, and it furnishes an 

 example of no less than three kinds of union. This 

 bone serves to form the basis of the cranium, and 

 concurs in forming the orbits, the pituitary sinuses 

 of the nose, the temples, &c. and to contain the 

 middle lobes of the brain. 



The Ossa Temporalia or Temporal Bones, (No. 5. 

 fig. 1.) are situated at the sides and inferior part 

 of the cranium, having an irregular figure, and 

 each divided into two portions : a squamous por- 

 tion, which is flat, and forms the squamous su- 

 ture, and a part of the side of the cranium; 

 and a petrous portion, sometimes termed the os 

 petrosum, which is very irregular, and is situated 

 at the basis of the skull. It is a hard, craggy 

 protuberance, nearly of a triangular shape, and 

 surrounds the organ of hearing, (which is contained 

 within the temporal bones ;) and below this petrous 

 portion is a concave angular projecting portion, 

 which forms apart of the lambdoidal suture. The 

 temporal bone has numerous processes, giving at- 

 tachments to muscles and tendons, &c. the most 

 important of which are the auditory process, or 

 outer bony circle of the outer bony passage, to 

 which the membrana tympani, and cartilage of the 

 ear, are fixed. As there is an anatomical descrip- 

 tion of the ear in the Encyclopedia, illustrated by a 

 cut, we have great pleasure in referring to that 

 article. (See Ear.) Each temporal bone is connected 

 with, or united to, the parietal, occipital, and sphen- 

 oid bones, and with the lower jaw. The substance 

 of these bones requires a little notice, as the squa- 

 mous portion consists of two tables and a diploe. 

 The mammary process of cells which communicate 

 with the cavity of the organ of hearing, and the 

 petrous portion is very hard and compact. 



The temporal bone, at birth, consists of three 

 portions, the squamous and petrous, already no- 

 ticed, and a ringlike Lone, which surrounds the 

 opening of the tympanum, or drum, of the ear. 

 The last bone is seen completely ossified at the 

 fourth month after conception: it is not a ring, 

 though termed annulus osseous, for its ends do not 

 meet. After birth, this portion is gradually elon- 

 gated to form the mcatus auditorius externus, or the 

 canal or tube which is terminated by a membrane 

 of the tympanum, and it is within the petrous por- 

 tion that the organ of hearing is situated, which 

 is perfectly formed at birth. 



These bones, with the sphenoid, unite as a cover- 

 ing for the middle lobe of the brain, and, as already 

 stated, afford accommodation to the organ of hearing, 

 and also concur in forming the temples and basis 

 of the cranium. A thorough acquaintance with the 

 anatomy of the temporal bones is indispensible to 

 the practical surgeon, particularly its cavities, fur- 

 rows, canals, tubes, &c., as it not only contains 

 the carotid canal for the passage of the chief artery 



of the brain, but likewise affords passage for the 

 portio dura of the seventh pair of nerves, with 

 other portions of the nervous system, as well as 

 the internal auditory passage, by which the nerves 

 of hearing have access from the brain to the ear 

 with the aqueduct of the cochlea, which serves for 

 the entrance and exit of the blood vessels of the 

 ear, and an entrance and exit for the internal jugu- 

 lar vein, &c. The temporal bones are likewise 

 very liable to be destroyed by venereal caries, and 

 we have oftener than once seen the whole of the 

 bone rendered worse than useless by this destruc- 

 tive affection, and even the bony parietes of the 

 tympanum of the ear have been sometimes almost 

 altogether annihilated by caries from common 

 abscesses, which most frequently occurs in scro- 

 fulous habits. An operation used to be performed 

 on the mastoid process of these bones, to remedy 

 deafness, which consisted in removing a portion of 

 the bone by an instrument of the trephine kind, 

 and forming a communication with the external air 

 through the mastoid cells with the cavity of the 

 tympanum. Another operation, more simple and 

 more certain, is perforating the membrana tym- 

 pani. The artery which luxuriates on the external 

 covering of the temporal bone, is frequently opened 

 in cases of inflammation of the brain, and its 

 course will be seen accurately delineated in Plate 

 LXXXVI. fig. 4. of Surgery. See Surgery in the 

 Encyclopedia. 



The os Ethmoideum, or Ethmoid bone, is situated 

 on the anterior part of the basis of the skull, be- 

 hind the root of the nose, and between the orbits, 

 and cannot be seen in any of the figures. It is 

 united to the frontal, the two nasal, the two su- 

 perior maxillary, the palatine, the sphenoid, and 

 the vomer, by harmony, thus having a connection 

 with not fewer than nine of the surrounding bones. 

 It constitutes a part of the nose, orbits, and cra- 

 nium, and forms an extensive surface for the organ 

 of smell. The ethmoid bone has a number of pro- 

 cesses, one of these is a cerebral or cribriform 

 plate, which lies horizontal above the root of the 

 nose, within the cavity of the cranium ; it is every- 

 where perforated by a number of small holes, or 

 foramina, through which the olfactory nerves pass 

 into the cavity of the nostrils. Another is the 

 crista galli, a process somewhat like a cock's comb, 

 which proceeds upwards from the middle of the 

 cribriform plate, and has attached to it the falci- 

 ~orm process of the dura mater. There are a few 

 other processes, but they are seldom noticed in 

 jractical works, either on medicine or surgery. 



At birth, this bone is mostly cartilaginous ; part 

 of the ethmoid septum consists, however, of bony 

 matter, and the superior turbinated bones are oc- 

 casionally found ossified. This bone is frequently 

 ;he seat of that destructive disease caries, of 

 ,vhich either syphilis, or its mode of cure, or part of 

 >oth, are most generally the producing causes. In 

 ;hese cases, the bone comes away by small portions, 

 f not timely checked ; but caries, and even complete 

 destruction of the bone, has also arisen from 

 tumors of the dura mater, and polypi in the nose. 



There are no muscles attached to, or covering, 

 ;he ethmoid bone. 



The Wormian, or Triangular Bones, are irregu- 

 ar bones, which are sometimes found in the course 

 of the suture, formed by the parietal and occipital 

 >ones. They are not constant, and received the 

 lame of a Spanish anatomist, who first described 

 hem. 



