Chapter Two—Morphological correlates
The sounds of language are certainly intimately related to the morphology of the vocal tract. A description of man’s vocal tract may account for certain peculiarities of universal features of speech.
（1）Face, lips and mouth
Comparative anatomy of the facial muscles helps us to explore the decisive factor of man’s face upon speech sounds. Huber (1931) demonstrated that all of the muscles of the face were phylogenetically derived from two basic muscular mantles which covered the neck and head of the prototype: the platysma (horizontal striae) the sphincter colli( vertical striae).
(請參考本書 P.34 圖)
The muscles themselves have undergone further differentiation in man, have grown in shape and anatomical distinctiveness, and show more intricate interlacing than in the great apes. That anatomical distinctiveness of the lips and mouth make possible rapid and air tight closure and sudden explosive opening, both being prerequisite for speech articulation.
（2）Topographical anatomy of oral cavity, pharynx and hypopharynx
In man the epiglottis is located much lower than in most other primates. It has been concluded that only man was capable of conducting the glottis-produced sounds through the oral cavity, whereas other primates had the sounds directed through their nasal cavity.
（3）Intrinsic anatomy of the larynx
Introduce the larynx structures of gibbon, orangutan, chimpanzee, and man. From the comparison we know the man’s vocal apparatus is in several respects simpler than that of the great apes. The geometry of man’s air spaces and fixed resonance chamber is “streamlined.”
（4）Relationship between peripheral anatomy and speech sounds
We can’t deny that there is a relationship between the morphology of the vocal tract and the acoustics of speech. But we have no data to indicate the cause and the effect in this relationship.
III. Central Nervous System
（1）Functional significance of form in the central nervous system
“Structure” in connection with the brain has quite a different significance than “structure” in connection with the skeleton or the periphery in general. In the brain, there are no independent parts or autonomous accessories. Any modification on the brain is a modification on the entire brain.
There are only a few histologically and topographically unique areas to which we can assign corresponding unique motor or sensory roles, i.e., the area of primary visual projection. There is no other area in the human cortex which is both histologically distinct and uniquely related to one and only one motor or sensory function.
(α) internal brain disease
This type of observation is the most unsatisfactory one because of the many cases in which the exact location of the lesion is only a matter of speculation.
(β) penetrating head injuries
Those show the somewhat random-appearing scatter of lesions and the overlap between aphasia-producing and aphasia-free lesions.
(γ) surgical excision
Surgical lesions are not commensurable, and the difference in effects cannot yet be interpreted.
(δ) observations of the exposed cortex
Stimulation experiments’ relevance to our understanding of the speech mechanism is limited because stimulation is a thoroughly abnormal interference with brain function.
（c）Summary: Language and Cortex
There is no evidence for an “absolute” language area, but the language function may be localized in statistical terms.
It is proposed as a speech hypothesis, that the function of all three cortical speech areas (Broca’s, Wernicke’s, and the supplementary motor speech area) in man is coordinated by projections of each to parts of the thalamus, and that by means of these circuits; the elaboration of speech is somehow carried out.
Even in the adult individual, where localization is more pronounced than in infancy, the right hemisphere may have some, though lesser, functions in language.
（5）Relative size of the brain
The variance of body weights is much greater than that of brain weights. The reason why a simple comparison of a few selected weights is not very revealing is due to the changing proportions of organ weights.
請參考本書P.70 Table 2.2