oned, agraphia is very often associated
with motor vocal aphasia.

A number of aphasic defects are met with in addition to those already
mentioned. Thus _paraphasia_ is a condition in which the patient makes
use of words other than those he intends. He may mix up his words so
that his conversation is quite unintelligible. In the most pronounced
forms he gabbles away, employing unrecognizable sounds in place of words
(_jargon and gibberish aphasia_). _Paragraphia_ is a similar defect
which occurs in writing. Both paraphasia and paragraphia may be produced
by partial lesions of the sensory speech centres or of the commissures
which connect these with the motor centres. _Object blindness_ (syn.
mind-blindness) refers to an inability to recognize an object or its
uses by the aid of sight alone. The probable explanation would seem to
be that the ordinary centre for vision has been isolated from the other
sensory centres with which it is connected. Not uncommonly there is
associated visual aphasia. _Optic aphasia_ was introduced to designate a
somewhat similar state in which, although the uses of an object are
recognized, the patient cannot name it at sight, yet, if it is of such a
nature that it appeals directly to one of the other senses, he may at
once be able to name it. _Tactile aphasia_, is a rare defect in which
there exists an inability to recognize an object by touch alone although
the qualities which, under normal circumstances, suffice for its
detection can be accurately described. _Amusia_, or loss of the musical
faculty, may occur in association with or independent of aphasia. There
is reason for believing that special receptive and emissive centres
exist for the musical sense exactly analogous to those for speech.

The speech centres are all supplied by the left middle cerebral artery.
When this artery is blocked close to its origin by an _embolus_ or
_thrombus_, total aphasia results. It may be, however, that only one of
the smaller branches of the artery is obstructed, and, according to the
region of the brain to which this branch is distributed, one or more of
the speech centres may be destroyed. Occlusion of the left posterior
cerebral artery causes extensive softening of the occipital lobe and
produces pure word blindness. Further, a tumour, abscess, haemorrhage or
meningitis may be so situated as to damage or destroy the individual
speech centres or their connecting commissures. The amount of recovery
to