506 



SCIENCE. 



[Vol. I., No. 18. 



If ice is found on the bulb with an air-tempera- 

 ture at or above freezing, it may be evaporated 

 by the air-current, or melted off with water. 

 The former method is preferable if the wet-bulb 

 temperature is below freezing. If, on immers- 

 ing, a drop is found at the bottom of the bulb, 

 it can be easilj- removed before it freezes by 

 touching with the edge of the reservoir. 



With these precautions, an accurate deter- 

 mination of the moisture in the air ma}' be 

 made ; and this must necessarily add to the 

 value of liygrometric observations, which are 

 so important in the study of the progress and 

 development of storms. H. A. Hazen. 



A STUDY OF THE HUMAN TEMPORAL 

 BONE. ^ — III. 



The temporal bone at birth consists of three 

 osseous pieces suturallj' connected and partially 

 anchylosed, butreadilj- separable. The pieces 

 are named the squamosal, petrosal, and tympa- 

 nal bones. In some animals they remain per- 

 manently distinct, and in others are vaiiouslj^ 

 anchylosed. The squamosal and petrosal cor- 

 respond in the main with the squamous and 

 petrous portions of the temporal as usuallj- de- 

 scribed; but the so-called mastoid portion is 

 derived from both the former. The squamosal 

 contributes about one-third to the mastoidea, 

 while the petrosal contributes the remainder. 



The squamosal is a nearlj' circular upright 

 plate which joins the petrosal at the petro- 

 squamosal sidure. This appears internally as 

 a fissure, extending fi'om the notch at the lower 

 border of the squamosal, in front, to the notch 

 at its border behind. Externally it descends 

 from the latter notch to a jiosition just behind 

 the tympanal. 



The mastoid portion of the squamosal is pro- 

 portionatety larger than later, and its auditory 

 plate is less distinctly differentiated from the 

 general plane of the bone. Internallj' it is de- 

 fined b\' a shelf on which rests the contiguous 

 border of the tegmen of the petrosal. Below 

 the shelf, the auditor}' plate exhibits the smooth 

 surface of the scute, which forms the outer 

 boundary of the attic of the tympanum. The 

 cellular portion above and behind forms the 

 outer boundar}' of the mastoid antrum. The 

 articular surface for the lower jaw is a shallow 

 concavit}', with scarcely- a distinction of glenoid 

 fossa and articular eminence ; and it deviates 

 relatively little from the general plane of the 

 squamosal. 



The petrosal obscurelj' displaj-s the labj-rinth, 

 alreadj- of mature size and bounded by compact 



1 Concluded from No. 17. 



walls, embedded in more spongy substance, 

 from which it Tasay be readily excavated. The 

 superior semicircular canal is especially con- 

 spicuous, and includes a large recess, which is 

 subsequently- obhterated. The tegmen appears 

 as a distinct triangular plate projecting from 

 the petrosal and overlapping the shelf of the 

 squamosal. The tympanic cavit}' with its attic 

 and the mastoid antrum are well produced, and 

 are of nearly mature size. 



The mastoid portion of the petrosal extends 

 behind that of the squamosal, and is commonly 

 partiallj' anchylosed with it. Its upper ex- 

 tremity is notched to a variable degree ; and its 

 lower part exhibits a comparatively slight emi- 

 nence, premonitory of the future conspicuous 

 mastoid process. 



The tympanal ^ is a horseshoe-like bone, 

 with its ends anchylosed to the auditorj' plate 

 of the squamosal. From this it slants down- 

 ward and inward, and is suturall}' connected 

 along its posterior and lower border with the 

 petrosal. Its inner margin is grooved for the 

 insertion of the t3-nipanic membrane. 



In the development of the temporal bone, 

 the squamosal and tj-mpanal are produced 

 from fibro-connective tissue, and the petrosal 

 and styloid process from cartilage. Ossifica- 

 tion commences in the squamosal about the 

 close of the second month of embrj'onic life ; 

 a centre appearing at its lower part, and ex- 

 tending upward in the squamous and mastoid 

 portions, and outward in the zygomatic pro- 

 cess. The following month, a centre appears 

 in the lower part of the tympanal, and grows 

 into a slender ring, incomplete above. Ossifi- 

 cation commences in the petrosal near the 

 middle period of foetal life. Two centres ap- 

 pear, and extend in the walls of the labyrinth. 

 These centres have been appropriatel}' named 

 by Professor Huxley the prootic and opisthotic. 

 They quickly coalesce to form the labyrinth, 

 by the subsequent continued growth of which 

 the pyramidal and mastoid portions of the 

 petrosal are developed. 



The prootic produces all that portion of the 

 petrosal seen within the cranial cavitj', except 

 that which is contiguous to, and forms, the 

 jugular fossa. It gives rise to the upper part 

 of the cochlea, including its base and cupola ; 

 to the internal auditory meatus, the upper part 

 of the facial canal and its hiatus, the upper 

 part of the oval window, the superior and 

 external semicircular canals, the upper arm 

 of the posterior semicircular canal, and the 

 tj'mpanic tegmen. 



The opisthotic produces all the petrosal seen 



1 Auditory procues, annuluB tympanicua. 



